When you call up Sprint, the first thing to do is ask for tech support right away. They are the only ones that can do it, customer service cant. Ask the tech support rep to change the "Call forward/Busy" and "Call forward/No Answer" fields to the phonefusion number. The Tech support rep will authorize and activate the feature. There is no additional charge for that service, according to them (unlike unconditional call forwarding at $0.20/event).
I hope this helps. It you have any further questions, feel free to contact [email protected].
This looks like a cool app. Its a shame we sprint users cant enjoy it. Is there anyone with a Sprint account that can confirm if it works without having to pay extra to Sprint???