If you read my blog from time to time, you know about Paddlespot. Paddlespot is a free service launched in the Fall of 2005, that aims to provide real-time river levels to whitewater kayakers on their mobile phones. We chose SMS as the primary technology, because it was the lowest common denominator- available on all phones.
The user scenario is pretty straight forward: Whitewater enthusiasts (kayakers, rafters, fisherman) simply send a text message to Paddlespot with the first three letters of the river name. Paddlespot responds instantly with the latest USGS river reading (we index that data). Knowing how quickly river levels can change, this information is much more valuable when you are standing next to the river. Previous to this solution, kayakers would check the web up to 2 hours before they would get to the river. Anyone who knows rivers can tell you how much can change in 2 hours, and how the safety factor can change as well.
Today Paddlespot continues to run, with a stable set of mobile users across the country - now indexing about 4300 rivers. Usage sways with the whitewater season, but has continued to grow steadily only by word-of-mouth.
If you know anyone who is looking to build a request-response SMS system as part of their broader offering, please pass this along to them. The Paddlespot code is a great starting point and will get them up & running much more quickly than starting from scratch.
Contact me with any questions neilcrist @ gmail.com.