How to Use Gmail as Your Central, Universal Communications Hub
All your communication is split between multiple services and inboxes—between your phone and your computer. Here's how to turn Gmail into the central hub of all your SMS messages, phone calls, instant messages, voicemail, and more.
Not only are our communications spread over multiple inboxes, but a lot of times, it's hard to refer back to those inboxes later. You have to know where you received a message, then go searching in the right place. What's more, the longer you let SMS messages build up, the slower your phone becomes; the more voicemails you leave in your inbox, the more difficult it becomes to sift through them from your phone. Luckily, just like you archive old emails in Gmail, you can archive your text messages, voicemail, and other communications in Gmail, so every communication you have is stored in one central location for easy access later.
This method relies heavily on Gmail and Google Voice (which is thankfully available for iOS now), so if you don't have an account already, go ahead and set one up. We'll mainly be using Voice to forward SMS messages and voicemails to Gmail. Coupled with a few other hidden Gmail features, we'll set up Gmail as a universal communication hub from which you can send, receive, and organize all your email, text messages, and voicemail, and set it up so you can view them all on one page. By the end of this guide, you'll have set up your Gmail inbox to look something like this (click to enlarge):
How to Use Gmail as Your Central, Universal Communications Hub
...creating an all-inclusive inbox for all your communication.

Setting Up the Services

First, we'll have to set up Gmail and Google Voice to send all of our messages to our Gmail inbox, and set them up with labels so we can organize them. You'll want a Google Voice account with your own number from which you send and receive calls to get the most out of this, so if you haven't done so yet, you'll want to set that up now. Then tweak the following settings to get everything forwarded to Gmail.

SMS Messages

SMS Messages are one of the biggest text-based forms of communication that most of us don't carry out regularly on our computer—unlike emails, IMs, Twitter or Facebook messages, and so on. That means they'll take the most work to migrate into your Gmail, depending on the services you use.

If you Use Google Voice

How to Use Gmail as Your Central, Universal Communications Hub
If you use Google Voice for all your SMS messaging, you're in luck, because it's just a matter of checking a few boxes. Just head into the Voicemail & Text section of your Google Voice Settings. Under Text Forwarding, check the box that says "Forward text messages to my email". Now, whenever someone sends an SMS message to your Google Voice number, you'll get it as an email in Gmail.
Alone, this is awesome, since you can reply to text messages right from your email. That means if you're at your computer, you no longer need to resort to typing on your phone's tiny keyboard to send text messages to your friends. Note that you can't initiate messages to new numbers through your email this way, but you could always head to the Google Voice webapp on the rare occasions you may need to do that.
Next, we'll want to automatically apply a label to incoming SMS messages, which we'll use later to create our unified inbox. Just head into Gmail's settings and create a new filter for messages matching From: txt.voice.google.com. You can also have them skip the inbox and get marked as read, if you're still using a more traditional SMS method (like the Google Voice app on your iOS or Android phone).
How to Use Gmail as Your Central, Universal Communications Hub

If you Don't Use Google Voice

How to Use Gmail as Your Central, Universal Communications Hub
If you're on an Android phone and you haven't yet switched over to Google Voice for all your SMS communications, a wonderful app called SMS Backup+ will automatically back up all your SMS messages to Gmail. Just head into the Market, download the (free) app, and open up the settings. We've gone through the nuances of this application before, so I won't get into it here, but it's a nice alternative if you aren't using Voice as your main number yet.
If you use this app, you can't send and receive SMS messages from your email directly like you can with Google Voice. However, you can still send them from Gmail's web interface by enabling a lab called "Text Messaging (SMS) in Chat" that will let you send SMS messages from Chat in Gmail. It sends them from a number your friends won't recognize, though it'll show your email address at the end, and their replies will show up in Chat for you.
How to Use Gmail as Your Central, Universal Communications Hub

Voicemail

We're going to use Google Voice to forward our voicemails to Gmail. Just head to the Voicemail & Text section of your Google Voice Settings and, under Voicemail Notifications, check the box next to "Email the message to" and add your Gmail address to the dropdown. To automatically add a labe, you'll need to create a new filter in Gmail matching From: voice-noreply@google.com and Subject: voicemail. Gmail reserves the "Voicemail" label for a Google Talk feature, so you'll have to use something else (I just use "Voice Mails"). It doesn't matter what it is, because when we create our unified inbox later, we'll have the chance to give the voicemail pane whatever header we want.
How to Use Gmail as Your Central, Universal Communications Hub
Next, head into Gmail Labs and add the "Google Voice Player in Mail" lab in Gmail. Now, you'll be able to listen to voicemails right from the email notification in the Gmail web interface, which will work great with our unified inbox.
How to Use Gmail as Your Central, Universal Communications Hub

Phone Calls

How to Use Gmail as Your Central, Universal Communications Hub
To integrate phone calls with the Gmail web interface, head into Google Voice's settingsand check the box labeled Google Chat. Now, when people call your Google Voice number, you can forward those messages to the Gmail web interface just like you would forward it to a cell phone. From the call window, you can also view your recent calls, which is handy. If you want to initiate a call from Gmail, just open up the Chat gadget and hit "Call Phone".
How to Use Gmail as Your Central, Universal Communications Hub
If you'd like to record a call and save it in your Gmail, you can do that with Voice too. If you're at your desk when a call comes in, you can answer it from the Gmail Web Interface and hit the record button to record a call. If you're on your cell phone, just hit "4" on your dialpad on any incoming call (sorry, you can't record outgoing calls), and the recording will show up in your Google Voice inbox.
How to Use Gmail as Your Central, Universal Communications Hub
You can't get these recordings automatically forwarded to Gmail, but since you're in control of what you record, it's pretty easy to remember to email them to yourself. Just navigate to the recording in the Google Voice webapp, hit "more" and then hit "Email". You can email it to yourself and apply a label just like you do voicemails or SMS messages for later reference.

Chats and Instant Messages

Gmail already has a great built-in feature that will log your Google Talk and AIM instant messages for you. Just head into the Chat section of Gmail's Settings and select "Save Chat History". Now, any Google Talk conversations you have (whether through the Gmail web interface or through an external client like Pidgin or Adium) will be saved in the "Chats" section of Gmail. If you're signed into AIM, it will also log those chats for you, as long as you are using the Gmail web interface to chat.
How to Use Gmail as Your Central, Universal Communications Hub

Facebook, Twitter, and Everything Else

Those are all the more complicated setups. Many other services, like Facebook and Twitter, have built-in forwarding tools so you can throw all those into your Gmail too if you want. For example, to forward Facebook Wall Posts, Messages, or anything else to your Gmail, just head to the Notifications tab of Facebook's Account Settings and check the boxes for everything you want archived in your email. If you want direct messages from Twitter forwarded to your email, you can do so from Twitter's settings: just go to the Notices tab and check "Email when I receive a new direct message". You can see the pattern here—anything that allows you to forward messages to your email can also fall into your "one unified inbox" with a few checkboxes (and Gmail filters, as described above).
How to Use Gmail as Your Central, Universal Communications Hub

Setting Up the Unified Inbox

To put it all together, we're going to use Gmail's awesome Multiple Inboxes feature, available in Gmail Labs. After enabling it, you'll still see your main email inbox in the Mail view, but with extra panes that we're going to use to show our SMS messages, voicemail, and chats (and whatever else you'd like).
How to Use Gmail as Your Central, Universal Communications Hub
To configure it, head into Gmail's Settings and click on the new Multiple Inboxes tab to configure it. For the first pane, type label:sms-messages as the search query, "SMS Messages" for the panel title. Of course, replace the label with whatever label you used for SMS messages. Do the same thing for the voicemail pane, and if you'd like a chat pane too, you can use the search query is:chat. I like to put my panels on the right side of the inbox, but you can also put them at the top or bottom of the Mail view—whichever works best for you.
How to Use Gmail as Your Central, Universal Communications Hub
Click on the image for a closer look at the Multiple Inboxes view.

Now, your Gmail inbox is far more than just email. You can send and receive SMS messages, listen to voicemails, make and record calls, and chat all right from the Gmail web interface. Furthermore, you can see and quickly access all your old SMS messages, voicemails and chats right from your main mail view, so you don't need to worry about deleting them from your phone. Of course, this setup is only limited to your imagination, since nearly every web service allows you to forward notifications to your email, so if you think of other services you'd add to your Gmail hub, tell us about them in the comments.