Babysitters and cell phones

I was just wondering what the thoughts are out there about babysitters using cell phones while babysitting my kids.  We had a 12/13 year old sitter for a few hours last night and when we got home my husband saw her texting.  The boys were in bed, so at first I didn't think too much of it.  I asked the boys this morning if she used it when they were up and they said "yes, a few times".  Is this a big deal?  Am I making something out of nothing?  I know when I used to babysit, I never used the phone to visit with friends while I was baysitting.  What are your thoughts?