If I were him, I'd be absolutely furious that you'd poked around in my mobile phone bills and then confronted me about it. The stupid phone calls are niether here nor there to be honest, but someone snooping in your private correspondance is an utter breach of trust and not something I'd tolerate. It's obviously not being unfatihful and as for demanding to see his other statements , do you really want to be in a relationship where you have to behave like this? He's a grown man, fully entitled to call stupid sex lines if he so wishes, and I wouldn't imagine he'd give a hoot if you call them too, because frankly it should be no big deal and certainly not a great drama.
If your relationship is good, this should be a non event, if it's not then look at why it's not and do something about that instead.