I've just read the thread about when you get charged for 08xx numbers etc. As it really isn't clear when you pick the phone up, what is and isn't free, I always go to saynoto0870.com and find an 01/02/03 or 0800 number there. Pretty much everyone you need to ring will have a geographic number on there. I use it also for calls from my mobile, as Orange charges you for an 0800 number!
I would expect most people know about that site, but just in case.
Maybe the mods could add this to the locked thread about 0845s and 0870s.