I can’t believe I missed this in my post about [1] useful phone numbers, but PayPal lets you send money via cell phone. Quoth [2] Lifehacker:

To start sending money from your phone, log into PayPal and associate your mobile phone number with your account. I know. I hate giving away my phone number too, but PayPal’s already got my bank information, so that makes the voice digits seem like less of an issue. Once you enter your cell phone number in your PayPal account and set up a mobile PIN (separate from your account password), PayPal’s voice robot calls your phone on the spot and asks you to verify the PIN. Once the PIN’s matched, your phone is PayPal-enabled.

Then, to send someone else’s phone $5.50 in cash, text message PAYPAL (729725) the message send 5.50 to 7185551212 where the recipient’s phone number is (718) 555-1212.

PayPal doesn’t exactly advertise this (it’s buried in their help pages), but you can PayPal someone’s email address from your mobile, too. Just make your text message send 5 to editor@lifehacker.com instead.

The cool factor is pretty good, but I could see myself using this on the run, for splitting checks and things like that. [3] Check it out.