Was with Vodafone, am a Virgin Media customer and about a year ago they offered me a really good mobile phone deal. Call Vodafone, 'we can match that' they said, less hassle I thought. Anyway the last 3 months of the contract they removed the discount, I called them, 'we are sorry you weren't told about this when you renewed' they said, it is our policy, nothing we can do..
Anyway eventually got some of the money back as 'goodwill' but have moved to a really good rolling contract with Virgin (£8.50 a month for 100 minutes, 200 texts and 200 minutes to Virgin mobiles) wanted to transfer my number and keep my phone. I called Vodafone, got my PUK code so I could transfer my number, gave it to Virgin, fab I thought that wasn't too hard.
BUT neither company warned me that my phone handset was locked to Vodafone, I had no idea, but I also need a code to unlock my phone. Called Vodafone who said that as I wasn't a Vodafone customer they couldn't help, 'go to an independent retailer' Googled, found a company, got scamed for £4 - brought 'unlocking report' not code, they sent me an email telling me to call Vodafone!!
Anyway more investigation I found that I could get a free sim from Vodafone, and so have ordered one which will make me a Vodafone customer therefore qualify me for unlocking code! What a palarva, no mobile for a week while I sort it all out!
Anyway moral of story 1) There are some fantastic deals if you want to save money
2)Check your phone handset doesn't need unlocking before you transfer your number.
Sorry long and dull but I wish I had know all that a week ago.