You can open a support ticket here >
http://support.fongo.com/anonymous_requests/new
This is all very strange and I want to say that it might be a problem with your cell carrier. The fact that someone else tried with a Fongo line is a good indication that there isn't a problem with your ATA though.
Have you tried *cough* mis-dialling your cell number to see if the call goes through (eg 123-456-7899 instead of 123-456-7890)? Obviously this might be an annoyance to whoever you get, but we all get wrong numbers from time to time, and you are only really interested in seeing it the number rings or not so you can put the phone down before they answer. **Disclaimer - This is not something that Fongo would suggest doing, it is just something I might do to run a test.
As for changing your number, sorry I missed that in your first post, the only thing you can do is open a new account and select the new area code you want (you don't need to buy the unlock key again). When you have the new account active, port this number from the new account to your existing one using this form
http://support.fongo.com/entries/535548 ... ngo-Mobile (*note there is a $5 charge). This WILL replace your existing number, so if you want to still keep that number you will have to look into something else.