Yep, same! I've been on the same £35 a month since June 2008 with the orignal iPhone! Mine ran out I think last September, but I always buy the iPhone from Apple - makes no sense really to keep the crappy contract I'm on. (Like you, I was just too lazy to change it!)
So from tomorrow when the new T-Mobile sim card arrives I'll be on a 30 Day rolling plan, one that I can cancel at any time for £15/30days getting 350 mins, a lot of texts and an impressive 1.5GB data.
I honestly think it's a fantastic deal, certainly love that I can cancel at any time and love the 1.5GB! But the biggest thing for me is I can finally get 3G at home, town and work. It means I can actually *use* my iPhone away from home!
Like you say though, I will miss the visual voicemail even though I probably get less than 20 a year!!
I could never get my BT OpenZone Cloud thingy working...ever...can't get it working with my BT account either... so thats not a factor for me