Suggestion

[usa2k]

OK, let me steal Rocky's product name, but call it Toll-freeway. Or maybe TOLLo?

Allow a 1-8xx number that when called asks for a 4 digit access number (Ideally the last four digits of your primary number (enough 1-8xx numbers as needed to keep that consistent.)

The caller will be routed through to the VOIPo number and ring the customer's VOIPo line. If the customer does not pick up, then its routed to Voicemail. CID of caller would show allow the VOIPo customer to answer. A message would tell the caller to hang-up and wait for their ring-back.

Depending on how much overhead that incurs, it may be possible as a free service.

Vonage, Broadvoxdirect, ... had web services where two numbers could be connected, but that needed www access handy. I don't think too many people found that helpful.