There are tons of uses for SMS (text messaging); Clickatell recently published a guide to 101 business uses for SMS. I'm still making my way through it, but it's a great read.
Read/Write Web last week posted a great guide to how SMS is being used for giving.
I tried one of the examples myself - this example with Verizon:
Starting today, customers of Verizon Wireless in the U.S. can donate to a charity called "Save the Children," who has mobilized in this time of crisis to provide lifesaving assistance in these two affected regions. Verizon customers can text to the address 4SAVE (47283) with the keyword "quake" to contribute to earthquake relief or the key word "cyclone" to contribute to cyclone relief. They will then receive a reply asking them to confirm their donation of $5.00, which will appear on their next monthly bill.
I tried it out, and it's easy as listed. My only complaint: there are links to Save the Children's site included in the texts, but clicking on it in the text message, it leads to a regular website, not a mobile-friendly WAP site. It's a missed opportunity for Save the Children, but a good start nonetheless.
I also wonder how Verizon's promoting this, as I'm a customer but haven't heard anything about it from them.
Note that R/WW lists a number of other ways to give via SMS; I highly recommend reading it in full.