this is a scenario
john take some BTC from the main wallet on the mobile phone whit a normal transaction
when john wants to pay whit BTC he can wake up the mobile phone client use the 3G to connect whit the network
using NFC john confirm and make the payment
i dont know if there is any limitation for accepting payments whit NFC by other phone, if i understand right how NFC works a mobile phone can accept and make payments
The current Android NFC API seems to be somewhat limiting, but I think a lot of people will try this in the future. Remember, the only information that really needs to be transmitted over NFC is the BTC amount to send, and the address to which it should be sent. Except for that the only communication is with the Bitcoin p2p network. But both Android devices needs to run a "real" Bitcoin client, or otherwise be connected to such a client. I think the best bet is to have real clients with real wallets, since it appears a bit scary to be connected to another bitcoind at home. You'd need to punch a hole in your firewall and such, which is a bit scary. Perhaps my worries are without merit, we'll see.