Unfortunately there is no easy way to do this. SMS is all routed based on phone numbers, and, unlike email, phone numbers don't have routing information built in. This means that you can't look at a phone number and know that it's Sprint or Verizon or Orange, so there's no way to know which carrier to send it to. So, first, you have to ask the user which carrier goes with that number, which is annoying, and if users are sending it to their friends, they may not even know which carrier.

The next problem is getting the message onto the carrier's network. Very few carriers have open, standard gateways for doing this. Usually you have to pay very high fees and negotiate access to get in. You can also send SMS by accessing their websites, but how you do that depends on each carrier's site. There is a perl module which has a lot of carrier info built in, so you might try that.

SMS is broken.

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