Non-Geo Numbers?
They're the biggest single problem, as far as I'm concerned.
I have a package suitable for my usage in terms of volume, I never go over my inclusive minutes. But I **ALWAYS** end up paying more due to 0800, 0845, 0870 etc numbers, none of which are included in the inclusive minutes, and are charged at normal rates on top.
It's fine when I'm at home, and I can look up alternative numbers, but when I'm out and about and need to call someone on one of those numbers fairly quickly, I end up paying extra. And 0800 numbers are never the quickest to be answered, so I'm paying extra whilst being told that my call is important to them. The "Say No to 0870" site is a pig to use when on a GPRS connection.
I find it unlikely that calling (e.g.) from my O2 mobile to a Vodafone mobile costs O2 so much less than calling an 0800 number that the first can be included in my bundle, and the second can't.