On the iPhone go to settings -> phone -> call forwarding and see if it's turned on. It's also worth going into "call blocking & identification" to make sure you didn't accidentally block people that you want to receive calls from.
First of all, when you make outgoing calls do they see the correct phone number on their side? Second, which phone do you own? I would check if you have call forwarding accidentally turned on to forward all incoming calls to voicemail.
