I've never done a check on a WG's phone number myself, but I don't see anything wrong with doing so. It's never crossed my mind before as I (perhaps naively) simply assumed they had punting phones/sims just as any sensible punter should have.
If she leaves an easily followed audit trail, then it's fair game for someone to follow it to her facebook page or wherever else if you ask me. What matters though is what you do with the information - outing her or otherwise intruding on her personal life is not acceptable in those circumstances as far as I'm concerned.
Anyway, that's my twopenneth, and if I ever get back to punting again, I'll still not be routinely checking their numbers out on google as who they are beyond being a service provider is of little to no interest to me.