The other thing that it could be is that this is a feature you have on your home landline that will require a number calling to show caller id to your home phone; if not immediate callback to that number will be done( to get rid of the pesky telemarketing few) this sounds like the iphone has caller id blocked and your home phone has a block for numbers that don't send caller id info.
resolution; find caller id to iphone and make sure it is on or call your home tel provider and refer to turn off anonymous call rejection, if not the vonage problem. Turn the device off after and let me know if this works. I had something similar to this.
