Next Big Thing on the Web - Free SMS Gateway
I woke up feeling a little prophet-ish this morning. I would bet you money, but it is illegal, so I am just going to say: I know what the next big service thing from Google should will be! Ready? It's a free SMS gateway that allows sending SMS messages through an open API.
Now think about it. Text-messaging ("SMSing") has been hot for a while now. Marketing companies and individuals are already using it big time. Text-messaging is expensive, though. Many little startups, with little, but interesting pilot sites just can not afford it. How is the industry going to innovate, if the innovators can not afford the tools?
There's a lot of data transmitted over text-messages and it could be even more interesting than the data you find in emails. Text-messages typically have less spam. If Google is willing to provide huge mailboxes for free, just for a chance to index e-mail text - they should be dying to get their hands on text-messages. If anything, Google is late to do it.
You say "privacy"? I say - yeah, like Google cares.
So, here it is - you should see something like it in the next 6 months. I give it a year tops.

How is this different...
... from simply emailing to the appropriate email-to-SMS gateway?
For example, verizon uses phone number@vtext.com (2024561414@vtext.com). A quick search of Google for "sms by email" shows lots of places to find the address, including, of course, a wikipedia article. Using one of these costs the sender the same price as the cost of sending email -- virtually nothing.
Knowing you, I'm assuming that you're envisioning something much grander than this.
Please elaborate.
E-mail Gateways Don't Cut It
Stating the obvious: if e-mail gateways were sufficient, the commercial SMS gateway service providers would not be able to charge so much.
The rest of the argument:
1) You have handful of e-mail addresses for major US-based providers; but do you have a reliable list with every cellphone provider in the world, that you would be able to send SMS if you were just sending from your mobile phone? You do not.
2) I am pretty sure the e-mail gateways will block your IP, if you keep sending "a lot" (by human measures) of messages.
3) There is no way to respond to a message one got from such e-mail gateway or properly identify the senders.
4) This is how message looks when it arrives:
Sender's Phone # 1(010) 1000-021
Message Text:
FRM: D*** H***
SUBJ: read my comment on freshblurbs
MSG:(sent via google's free sms gateway -- gmail)
You can see the many problems with it that can be disregarded when it's just a quick message from a buddy of mine, but can not really be used in a "serious" (such a bloated word, but nevertheless) text-messaging-based campaign.
What are we looking for?
A proper REST API that assigns each API account with a numeric code that cell providers would interpret as a proper cell number (not necessarily an actual number in any actual country though). The API should allow sending well-formatted text-messages that will look just like if they were sent from a cellphone. The API should also allow checking list of latest messages on the server - incoming text messages.
None of these should be a problem for a company that has as much resources as Google does.