Phone ettiquette I totally agree with this post.
As someone who has to deal with customers who come to the counter chatting on the phone I can recomend one thing.
Ignore them.
Find something to do, furrow your brow so they know it must be important, don't make eye contact, and count.
My best time is 45 seconds which by that time they will have said "excuse me" or something similar. I surmise they must be talking to their friend and keep ignoring them. If you should be blessed by other customers, greet them with great gusto and serve them before the phone user.
If at anypoint TPU try to attract your attention whilst still chatting, tell them you will wait until they finish their conversation, remaining cheery of course, and hopefully gleefully serving everyone else.
I've used this recently, on a minor celebrity who I mis-recognised (I thought she was a regular customer). Turned out to be Mylinkers (no google juice cos you're not a very nice person) who was in town filming Most Haunted, as told by one of the local bouncers. She bought a Snickers and a copy of Heat. Eventually.  ¶ Wednesday, June 28, 2006