1. A system for off-loading telephony connections for a multi-mode phone from a cellular network to a computer data network, the system comprising: a receiver receiving a request for an outgoing call from the multi-mode phone having an originating phone number; a controller for determining, in response to the received request, if the multi-mode phone is reachable via the computer data network; and a bridge for bridging a call between the multi-mode phone and a destination of the request for the outgoing call when the multi-mode phone is reachable via the computer data network by (a) receiving at the bridge, from a Service Control Point during call setup, a first Mobile Station Roaming Number from a pool of available Mobile Station Roaming Numbers, where the first Mobile Station Roaming Number is different than the originating phone number, (b) establishing a first call from the bridge to the multi-mode phone using the first Mobile Station Roaming Number, (c) establishing a second call from the bridge to the destination of the request for the outgoing call, and (d) connecting, by the bridge, the first and second calls, wherein the bridge communicates with the multi-mode phone via the computer data network and the destination of the request for the outgoing call via a public switched telephone network.