o2: July 2008 - January 2010 on iPhone 3G. No problems with voice calls, but data always patchy, usually only had EDGE enabled.
Vodafone: January 2010 - September 2010. iPhone 3G, then switched to iPhone 4. Had issues with voice calls, would have lots of dropped calls and often poor data speeds. Was able to make some Skype calls over 3G, and a friend with an iPhone 3GS also able to make Skype calls.
Orange: September 2010 - Feb 2011, iPhone4. Was excellent at first, or so I thought. Voice calls great, but data patchy, difficulty with Skype over 3G. Would show 5 bars 3G but 'slow data network' warning with Skype.
Vodafone again - present. Had missed calls again, even when I was outside or in the car. Tried calling from Skype with 5 bars 3G but it wouldn't work, seems like data is poor. Don't know what to do anymore...
Edited by Saltank (Tue 15-Mar-11 21:03:01)