Swappa has launched a new, free ESN Check (Beta) service. http://swappa.com/esn
Use the service to validate with carriers to ensure ESN / IMEI / MEID is clean for activation. Currently works with Verizon, Sprint, and a few other (CDMA) carriers. Still not much help for GSM carriers, but I'm working on it.
Swappa makes it easy for anyone to buy and sell fully functional, gently used Android devices.
