Most of you out there have an email address that is a total of at least 16 characters long if you include the @, the dot and the TLD (com/net/org/etc.)
Being that mobile internet is rapidly becoming more common, a super-short email address can come in handy because it takes much less time to type on a cell phone or smartphone, and furthermore won’t word-wrap when entering it in on smaller screens.
To note, I’m not suggesting you switch to any of these (although you could), but having a secondary "mobile-only" address is convenient.
You can register a free email address here at http://mail.in.com/. This is a very good mail provider. Setup is easy, the interface is simple and well-designed (the tabs work great), and you’ll be up and running in no time. In.com is very modern and you’ll appreciate the way it works.
9y is Hushmail-powered, so you know it’s secure. This mail provider offers a very stripped down and basic interface, but it does the job. The free version only allows for 2MB (not GB) of space, but for mobile use that’s more than enough for just text.
V.gg is the shortest of the short I could find concerning free email that’s available right now. I have no idea how reliable this email service is as the web site looks very old and has a (C)2005 notice at the bottom, but, it’s there and you can get one.
GMX has several different TLDs besides COM, one of which is DE. This is the "longest" of the short-address providers. And GMX is well known to be stable and reliable. You can sign up for a COM account first, then add in a DE afterward from within the account control.
Using your own three-letter domain
"But all the three-letter/character domains are gone."
Not by a long shot. If you want one, there are plenty. You won’t get a dot-com, but there are plenty of NETs and ORGs to choose from. For mobile use it truly doesn’t matter what you have as long as it’s short.
The only thing you should take into consideration is not to use numbers that would confuse anyone.
For example, if you look at the C’s, C50.org would be a bad choice because the 0 (zero) could be confused for the letter O. C55.org or C66.org on the other hand would be much better choices.
It would also be advisable not to use letters and numbers next to each other that look similar, like S5 or 5S.
Being that you only want this domain for mail-only use, the best way to accomplish this is by using Windows Live Admin Center, which is Hotmail, or Google Apps Standard Edition, which is Gmail. This used in concert with a service like EditDNS will allow you to set up mail for free without any hosting costs whatsoever. The only cost will be the annual $10 to $20 domain registration fee.