I'm making a lot of assumptions here but it sounds like you're being over protective and you may have had issues in the past with that type of behavior.
I can't imagine wanting to call my wife while she was out with her friends. I can imagine spending that time riding, playing X box 360 or maybe watching porn but definitely NOT calling her!
I don't trust women. At the same time, I would never motivate them to violate my trust. I've rarely met a woman (or human for that matter), that will stick with you through thick and thin if something better (richer, funnier, better looking, more secure, willing to spend more quality time etc...) comes along. So be everything your woman wants you to be (within reason i.e. no toys allowed in the rear end), and trust should never be an issue.
In this case, that means giving her space and being really secure about it.
I wouldn't worry about it if that's the case (unless you have a reason not to trust that friend's influence over your lady). If it was a platonic friend I was gonna go this route:
[ame=http://www.youtube.com/watch?v=zywIR_ZFLts&t=1m3s]Chris Rock - Women's Platonic Friends - YouTube[/ame]
My dad and his wife (not my mother) have been married now for 31 years.
They BOTH tell me the secret is to stay the hell away from each other (actually my step mother said "we're not up each other's ass all the time." Eloquent woman in my opinion) reguarding day to day things.
Of coarse household stuff and intimate things require both to be involved but that aside...be independent of each other. You'll be together for ever.