1. sign up for gizmo
2. sign up for grandcentral
3. configure grandcentral to use your gizmo 10-digit phone no.
4. configure rtcomm for sipphone.com using gizmo phone no.

free incoming calls: landline calls to the grandcentral phone no. => ring the tablet as an internet call (voip)

free outgoing calls: calls from the grandcentral.com address book (or inbox) => ring the tablet as an internet call (voip) => ring the lineline

Enjoy!

Note: if flash player is not available, use grandcentral.com/mobile and select gizmo no. as your mobile number.