Well, you could try Callcentric, which has good customer support (only via email), is US-based, and has plenty of porting experience.
VoIP numbers are considered land lines for porting purposes, and land line number porting is somewhat more complex than simple mobile-to-mobile ports. You will generally need to contact the losing carrier first, and confirm that your numbers are portable (not in a carrier-locked condition), and deal with any procedure they might have to give them your permission to release the numbers. You then contact the gaining carrier (Callcentric in this case) and submit everything they need. They may ask for you to complete a Letter of Authorization (LOA) form, along with submitting the telephone numbers, account number(s) and some sort of PIN or password. They may also ask for a service address. I mention this because you were having trouble with
voip.ms; not necessarily to defend them, but to point out that the process (as defined by the FCC and administered by NPAC) is pretty rigid and unforgiving of errors.
