I'm looking for a sipphone application that can handle multiple sip providers and connect to multiple providers at the same time, so that if someone calls one of my accounts, it rings regardless of which provider is currently configured for outgoing calls.

Phonerlite, as I understand it, can accommodate several accounts, but it only rings for the one that is now active.

Zoiper claims that the free version is not portable.

Any suggestions for a free portable sipphone?