Google today announced Google SMS beta, a service that allows mobile phone users to search Google via text messages. Just send your query to 46645 (GOOGL on most phones) and you'll get back results in another text message. Currently the service is US only.
With the combination of phone look up (or even reverse lookup), local results, Froogle, the built in calculator and more, this is a powerful service. See this page for some search query ideas.
Example
MobileTracker just tested this service on Verizon Wireless network and T-Mobile USA. We sent 46645 the message:
5 acres to square feet
In a few seconds back came the reply:
Calculator by Google: 5 acres = 217800 square feet
Typically mobile phones come only with simple calculators that could not do this conversion. Teachers should be on the watch, math scores are bound to increase.