You can use Sipsorcery instead of a VOIP provider. Sipsorcery allows you to continue using GV via the callback method after the drop dead date.
For an explanation see:
http://www.obitalk.com/forum/index.php?topic=7327.0Here is Sipsorcery's Website:
http://www.sipsorcery.com/mainsiteAccording to giqcass in the above Sipsorcery explanation you can only have 3 simultaneous calls at a time, so you might need 2 accounts each at $69 per year or one professional account at $199 per year. You would then need 4 or 5 DIDs.
You would have to setup a fairly complex Dialplan using the Ruby programming language. They have a forum where you can get help or I can help.
This is what I'm going to use after May 15th.
The unknown is how long Google will allow the GV callback method.
Edit:
You can test Sipsorcery with your current setup. They also have a full refund if you cancel within 60 days. You can get free DIDs from IPKall or IPComms to test, but it's probably not a good idea to use them for a business.