This is the third in a series of relatively short posts of potentially crazy, potentially profitable ideas for musicians to use. If you use them, you don't have to give me any credit, but please do write in and tell me how it worked for you.Here's an idea that is best enabled with Topspin, but is worth running by any means necessary. Get a phone for the band (or, alternately, get an SMS receiving number/account online), post the number at concerts (tape it on your amps for full effect), and have fans text you their e-mail addresses. At the end of the night, or in the van the next day, compile all the e-mail addresses (and their phone numbers) you received. Put them into a list titled the city or venue you just played so you can keep track of where they are for future communications.
Finally, give them a reward! My recommendation is a private link to a video of the previous night's performance, but I know not everyone travels with video cameras (you should! get the merch guy or someone in one of the other bands to tape you). Alternately, a personalized message would be nice, an exclusive song download would be better, and encouragement to tell their friends if they had a good time is always good policy.