When I was part of a duo, we had a simple way of dealing with it; we would ask, politely, before we started that phones should go on to silent, so as not to disturb people who wanted to sleep during our set. This usually got a laugh, but got the message across. If a phone went off, the first time we let the audience deal with it; lots of 'shhhh, there's people trying to sleep here' and so on. If it happened a second time, we would instantly switch from whatever we were playing to the 'Nokia tune', with the explanation that 'this one seems popular tonight'. Again, usually a laugh, message sent, and on with the show. Worked for us, without antagonising the audience. Shaky eggs were a different matter...
I think you have to accept that there will be people there who really do have to have a phone switched on, and work around it by asking them to use silent settings as suggested by Mr Red above.
Tim