As I work part time in a supermarket I can understand exactly where both sides of this argument are coming from....
To me there is nothing particularly wrong about using a phone whilst at a checkout because at the end of the day who knows how important that phone call could be to that person, however I do feel it should be a on courtesy to at least say hi, generally respond to any questions and at the end say Thankyou....
However, as my store has self service checkouts when I am on my break I spend most of it talking on my phone and tend to use these rather than have the awkward half conversation with people who (quite often) don't care about their jobs and least of all customer relations :/
Whenever I am in store I feel it necessary to try and keep customers as happy as possible and to all intents and purposes I feel I do this well, but once again you do get difficult customers which assume, seeing as you work in a supermarket, that your level of intellect is comparable to road kill :/ I mean my job there is part time and I've been there for almost 3 years and not only that but I'm currently doing a double honors degree in 2 sciences XD I mean I like to think that I have enough brainpower to stick my hand in a fire and I oh god that's hot I ought not do that again rather than sticking my hand back in to jut double check that it's hot
Which is how I'm coming to conclude this rant.... Most staff seem to be stereotyped by a few customers who think they know the world better than others.... And I think it's wrong to say that manners are "on the way out" but I do believe that 95% of customers are the nicest of people and will generally go about their shopping without any complaints, questions or general moanings about staff... With the other 5% being rushed/irritated/tired etc etc
It do believe however that kids are getting worse every year and it seems as if good manners may be a thing of the past at the rate that children begin to curse, get angry and sometimes violent for not getting what they want... But at least they're kids and not adults who have to change the habit of a lifetime, indifference and intolerance :/
But still... People aren't all the same and although I do agree in principle with your point about how manners are slowly but surely seeming less valuable in day to day life... I am a heavy believer that trying to be at least considerate is the way toward a more tolerable society
Rant over XD