Hi: Sorry that I didn't see this question Don. I have a contract with a company called VoIP.ms. The other service I've wanted to look into is SIPStation.
With VoIP.ms, I set up my RaspPBX as a trunk service, rather than as an endpoint. With any incoming calls, they all get routed to the RaspPBX for handling.
Within the RaspPBX, the incoming call gets sent to an interactive voice recording, which requires a person to press 5 to proceed (think of it as a vocal captcha) I filter all of telemarketing calls this way. Once past the IVR, my fixed home phone and the household's cellphones make up a ring group which gets rung with the incoming call.
On the whole, once I got past the pains of figuring out how to set this up, it has been a fairly maintenance free system.
I setup this system about a year ago along with an ATA adapter to connect our legacy cordless handsets. Our cellphones via softphone software make up the additional internal extensions on this network. The raspberry PBX is connected to a VoIP service provider and we've retained our old phone number. The PBX handles our voicemail, answers incoming calls with its digital attendant, and rings both the legacy and the cellphones to connect calls. This system works very very well.