Hi that is what started with my husband, although I had previous experience of him doing the same thing and was proven that he was having an affair, this time i just asked him to respect me and tell me the truth, he basically admitted he had kissed another girl, may not sound much, but a second time round destroyed what trust I had, your wife has something to hide if she does not leave her mobile around! trust your instincts they are probably correct, ask her outright, the truth does hurt if it is something you dont want to hear, but surely you are worth more than what this sneaking around is putting you through!
Hope you work it out.