The security bit is a different issue, and needs to be addressed seriously.
I have a MaGlobe account, which I use heavily when visiting the USA. It's cheap there because landline calls are mostly cheap. It's not so cheap in the UK - and the UK "Freefone" number it offers doesn't work (I think it's an old AOL one that's been discontinued, but nobody told MaGlobe).
I've not researched the topic since I got my MaGlobe account, because I'm happy with it, but when I did, it was dramatically cheaper than any of the other options, didn't require such large upfront credits, and the credits don't expire so quickly - as long as you top up with the minimum amount about once a year.
A friend of mine who globetrotted used AOL, till he found out what I was paying MaGlobe...