Let's rehearse a few important lines, shall we? Repeat after me:
"I'm sorry, I have to hang up now because I'm getting into a crowded elevator. I'll call you back later."
"Hi, I can't talk right now, I'm driving. I'll call you back later."
"Hi there. Sorry, but I'll have to call you back later. I'm at the table with a friend."
"I'll text you back later, I'm at band rehearsal and my section leader told me to leave my phone in the car."
Please use these liberally, so that I am not forced to take your cell phone, stomp on it repeatedly, and shove the broken pieces where the sun don't shine. Thank you.
PS - There is no line for store clerks because if you are on the clock and have a customer, you LET IT GO TO VOICEMAIL YOU STUPID PIMPLE-FACED PUNK!