When Apple and AT&T announced that iPhone 3G service plans would not include SMS (Short Message Service) text messages with the base plans, and SMS messages would be billed for either individually or in prepaid blocks, I was annoyed, along with pretty much everybody else. To make the highway robbery even more egregious, AT&T (like many other cellular carriers) now charges SMS recipients, as well as senders.
That's why I was delighted when Jeff Carlson pointed out that AIM on the iPhone could send SMS messages for free (see "Send SMS for Free via AIM on iPhone," 2008-07-13). Unfortunately, the iPhone AIM app is lousy. It's unstable, and messages I send from it are rarely received.
However, several alternatives exist for both phones and computers. Note that these vary by cellular carrier - I concentrate here on AT&T options that work in the United States; your mileage may vary elsewhere.
Method 0: Plain SMS -- You can send SMS from a phone. 500 SMS messages are included "free" with the standard AT&T data plan for the original (EDGE) iPhone. For the new iPhone 3G, the base data plan doesn't include any SMS messages. You can pay $5 per month for 200 messages, $15 for 1,500 messages, or $20 for an unlimited number of messages. Or, if you don't plan on sending and receiving more than 25 SMS messages in a month, you can pay $0.20 per message by not signing up for any plan. Astronomically expensive!
Method 1: AIM-to-SMS Gateway -- For computer users, Jeff's method is fine - AOL's AIM-to-SMS gateway works consistently. My issues were with the iPhone AIM client. On the Mac, iChat and AOL's Mac client are reliable, and another iPhone client using AOL's IM service would presumably have been fine. This morning, in a quick search for "AIM" in the iPhone App Store, I found 5 chat clients that claim AIM compatibility. But I barely use instant messaging since I started using Twitter, so determining if they work more reliably than the iPhone AIM client is left as an exercise to the reader.
Method 2: Email-to-SMS Gateways -- My favorite way to send SMS messages to iPhone-using friends is via email from either my Mac or my iPhone to their 10-digit cellular number @txt.att.net. txt.att.net is AT&T's email-to-SMS gateway; it generates an SMS message that looks something like an email message, with minimal 'FRM' & 'SUBJ' headers adapted from the original message, and forwards that as an SMS message to the specified 10-digit cell phone number. Longer email messages are broken into multiple SMS messages. Now that I realize my iPhone 3G-using recipients pay for incoming SMS messages (including gatewayed spam!), I'll probably use this approach less, and avoid long messages which would be fragmented and thus charged as multiple SMS messages.
Email-generated SMS messages are easy to recognize - they come from strange-looking phone numbers, like "1 (010) 100-010" for the 10th message I received from the gateway.
Unfortunately, these gateways are generally specific to individual carriers - AT&T's gateway works only for AT&T subscribers. Teleflip used to offer such a multi-carrier service, but the company has gone bankrupt. Notepage offers a long list of gateways. If you're not sure which gateway to use, try sending an SMS message from your phone to your email address (which will likely entail an SMS charge on the cellular bill) - the email should show a valid return address at the appropriate SMS gateway. Some SMS programs allow this, while others accept only phone numbers as recipients.
Method 3: SMS Web Pages -- Many cellular carriers, including Verizon Wireless and Sprint, offer public Web pages for sending SMS messages to their subscribers. In contrast, AT&T's page is available only to logged-in AT&T customers, although hopefully that means it can reach any SMS number. I am not aware of a Web page which enables non-AT&T subscribers to send text messages to AT&T subscribers.
Method 4: SMS Applications & Widgets -- There are a variety of applications and Dashboard widgets that you can use on a full-fledged computer to send SMS messages. Many of these charge the sender, although they appear to operate across cellular carriers. I suspect they use commercial gateways which have the same access to cellular providers as other providers, but nobody except AOL appears to do this for free.
Method 5: Mobile Phone Under External Control -- Additionally, several Mac programs exist that can instruct a mobile phone to send SMS messages, generally via Bluetooth or USB. The VersionTracker link immediately above lists a few. Obviously, there's no difference in price when using this method, but it may be easier to type out a message on a real computer keyboard.
MMS: Multimedia Messaging Service -- In addition to SMS for short text messages, MMS enables mobile phone users to send one another pictures and short videos. The iPhone lacks MMS support, although Mail is perfectly suitable for sending attachments to an MMS gateway, if you'd like to reach a non-iPhone cell phone that does support MMS. Messages sent to iPhone cellular numbers via @mms.att.net are silently dropped.
SMS messaging may not be used in the United States to the extent it is elsewhere, but I hope these resources make it a bit easier - and cheaper - to stay in touch with friends and family.