I don't know why I thought you could do this but I thought I'd check. Can you use the on board phone/remote to call other passengers on other parts of the plane?
Yes, but ONLY if they've enabled their phone to receive calls (the default is off). So, if you know you're going to want to call - arrange it beforehand!
If your on a V:Port A/C you can also use the seat to seat message service for free too and that doesn't need switching on at the other end first either. You just need to know the seat number.