Great list, especially for people that tinker all the time.
Interesting quote from RNK:
"We are partnering with newspapers, online classified companies and others,said Kevin Rohnstrom, senior vice president of new product development for RNK. We provide temporary phone numbers at low cost, and customers keep them for as long as needed. The idea is to do it for small dollars and large volumes." –Kevin Rohnstrom, Director of New Product Development ...on RNK's new product: MyTempNumber... (Telephony Magazine)
BTW, while tinkering is great fun for you, please remember to spend as much time marketing and selling as you do on tinkering.