Then why not get a VoIP ATA adapter and use your Beocom as if it was still connected to PSTN? Simple as that, and not horribly expensive either.
It's not that simple if you want to use both VoIP and PSTN, but at least here in Finland, people are getting rid of PSTN lines at an increasing pace, and even the providers are starting to wrap up their copper in remote areas...
-mika