I investigated using Callcentric to replace my POTS telephone. (I later abandoned my attempt to port my existing POTS number to Callcentric but still plan to use them for international outcalling) I wrote a Python commandline client for their "click 2 dial" service.

To use it, create a file in your home directory called ".callcentricrc" and populate it with your callcentric credentials in the following format: 

login = "example"
password = "s3kr1t"
moderator = "1777MYCCID(EXT)"

Then run the program: 

c2d.py 17771234567

Or select a different moderator by 3-digit extension or by full 1777MYCCIDEXT number: 

c2d.py 17771234567 101
c2d.py 17771234567 1772222222101

Files currently attached to this page:

c2d.py3.2kB