Fairweather fan said it perfectly, and Thirstyboots gave good advice... but my suggestion is try to not making a big deal when you sit down with your wife, if she gets the idea that this is so important, she'll freak out even more. I mean, the big deal is not the message itself, but the kind of intimacy which texting "non business" messages it could lead to. It's not a bad thing per se, because you can have female or male friends and share a lot with them, but in this case your wife seems to perceive this as a threat.
I wouldn't set the stage to talk about this, like going out, because she could get the notion there's more to it than an innocent text message. I'd talk to her straight and ASAP, and ask how she feels about it, and then seek together for the best way to chill things out. Every person needs some security, and unless it involves hurting anyone, you've got to help your wife feel you're together in this little thing as it will make her feel sure about the big things. Whether is keeping all contacts through your wife or any better solution, do it together and it will be ok.
Nothing kills a relationship quicker than suspicion and things like checking the other's phone/facebook...
Hope it works perfectly, cheering for you and your family.
