I try super hard to not be on the phone if I'm going through a checkout and I'll ignore my texts when I get them while I'm in line. If I'm on the phone in line (I know it might be rude) I make every effort to pay more attention to the cashier than the person I'm on the phone with. This has been as simple as "hang on so and so, I'm in line at the grocery store and I'm trying to pay" or I've gotten off the phone. However I usually find for a conversation that has the potential to keep going that it's easier for me to just say "hang on" to whoever I'm on the phone with than go through the whole getting off the phone just to pay thing because it's easier for me to set the phone down on the counter, pay, then pick it back up than having to say goodbye, lock my phone, and find room for it in my purse really quick. I seem to have gone off on a bit of a tangent and I know I'm probably in the minority, but that's how I am.
As for being out in public in general with phone use, I'm pretty neutral. As long as I'm not being bothered, it doesn't really bother me. Talking/texting during a movie is going to irritate me, talking loudly on the train or bus is going to bug me, but just walking down the street I don't really care.