I avoid talking on the phone on public transport at all and do use the phone against my ear if I have to take a quick call for some reason. But otherwise, when not on public transport or around strangers, I only use my mobile on speakerphone.

It's partly physical - fucked shoulders make holding a phone up to my ear really difficult - and partly habit. It actually feels slightly weird to hold the phone to my ear like an old-fashioned phone (please see previous paragraph before getting annoyed at me). The habit part is probably why for most people, but I guess you can never discount disability.

Whatever their reason for using speakerphone, if it's a quick and practical call then I don't find it that annoying to overhear. Even if that does mean you sometimes overhear stuff that's far too personal, and least it's over quickly. For you, at least. Little Jimmy's Mum will have to put his uniform in the wash the second they get home and maybe have a talk about how to use the toilet.

When people chat and chat as if they were in their living room, it's really rude. I sometimes feel like joining in, since they've made me part of it already.