Interesting. Some time ago O2 suggested that they would introduce free incoming roaming, but it is a pity that they have put a monthly charge on it.
http://www.o2.com/media/press_releases/pre...asp?archive=yes
http://www.o2.com/media/latest_pr_2182.asp
Whilst 35p a minute is not that cheap, it is about the same as most global SIMs rates for calling mobiles (59c), and not everyone uses different callback ...