HN: Please help me make this (or tell me if it exists)

A small device to plug a phone landline into that also runs Asterisk and accepts SIP/VoIP phone registrations over a WiFi. Couple this with an iPhone VoIP app and iPhone now replaces a home phone.

For an extra bonus allow the SIP app to connect to the home LAN over the Internet (and I am willing to jail break my phone for this).

PS. Don't want a service like MagicJack, but rather a standalone hardware device.