Well it depends on what you mean by keeping in contact.

Think about these scenarios for a minute:

--Would you object if they wish each other happy birthday and otherwise are not in contact, ever?

--What if she talks to guy friends online? Nothing romantic, facebook friends.

--What if her next-door neighbor growing up was a guy, is it okay for her to see him?

--What if she asks a guy at work to help her with something?

I don't think that trying to isolate her from guys is the right path to be on.

Do you trust her or not? If you can't trust her (or vice versa) then you two shouldn't be together. But if you do trust her, then trust her. Don't be going through her phone, don't be interrogating her over guys.

Think about who you want to be:

--Do you want to be the kind of guy who goes crazy with jealousy when his girlfriend comes near any other guy?

--Or do you want to be the kind of guy who knows his worth and stays calm about his girlfriend?