Calls to a women he has dated before

Why are you looking at your husband's text messages? I would be very upset if my wife did this to me.

Yes, it's inappropriate, sneaky and wrong.

But so is looking at his text messages.

Is that the ONLY way you found out about this. Something is wrong with your relationship. Look at that - not his phone messages.

Yep, he is wrong to continually contact her regardless of the method of contact. But as others have said, even in a marriage there has got to be some expectation of privacy. You should not have been snooping in his phone.

Have you tried sitting down with him and talking to him about how his communications with this other woman make you feel? That would be the place to start. Maybe begin the conversation by apologizing for snooping around in his phone and then going from there, telling him how you feel about his contacting this other woman so much.