I have been helping some clients with some direct mail campaigns and the results are typical. About 1% response and about 0.5% close ratios. Doesn't sound good, but when you mail out 1000 pieces at about $0.30 each is $300 to talk to 10 people and to get 5 sales. That's a $60 customer acquisition cost. Actually, not bad.
There are places to get good lists like Melissa Data, Marigold Tech, and Harte-Hankes. Harte-Hankes is an expensive, but detailed leads list and should only be used with an experienced tele-sales person for high-margin services.
Direct mail is about two things: targeting and repetition. You need to keep sending out the mailer. Verizon sends me one almost daily for FiOS. A different mailer each time - postcard, letter, carbon envelope, yadda. And it needs to be going to folks in your demographic. For example, your tower has signal there or out of the Central Office you are collocated in.
More to come about direct mail over at the Marketing Idea Guy.