We recommend CallCentric for our customers so long as you do not plan to use call transfer. There service is generally good but due to a bug in their system cannot implement call transfer.
Callcentric allows you to make and receive phone calls over the Internet with no signup or monthly fees. They also offer a paid service which lets you choose from a USA or Canada phone number and offers excellent rates when calling to real telephones.
Sign Up Here: www.callcentric.com/signup/.
|SIP Number/Username:||[Your CallCentric Number]|
|Password:||[Your CallCentric Password]|
|SIP Proxy Server:||callcentric.com|