Google Mobile allows you to search for several different types of information using only the text messaging (SMS) feature of your cell phone. This is incredibly helpful when you're out and need to know an address and phone number, the weather forecast, where to get a pizza or flowers, measurement conversions, scores, movies time or any one of several other bits of small, but important information.
To use the service, just address a text message to GOOGLE (466543), enter your search query, and send. Usually the form of the query is either the type of information, followed by your request (e.g., "define aquarium" or "score browns") or the subject followed by the zip code ("pizza 44691" or "movies 44805" or "park street brethren ashland oh").
You can play around with the search process and the type of results produced on a virtual phone at the Google Mobile site before trying it on your phone.
The odds are pretty good that your cell phone and carrier support text messaging on a pay-per-use basis, usually $0.10 to $0.15 per message, even if you don't have web access or a text messaging package with your plan. A typical interaction with Google Mobile will involve 1 outgoing message to ask the question and 1-2 incoming messages with your answer. Not free, but still better than a call to information.
When you're out doing visits and need a phone number and address or need to get the name of pizza place where you can pick up pizza on the way home from a late meeting, this is an invaluable tool.