I was told that I needed to change the simm card in my phone for a new one, this due to changes in the network. I duly received a new simm card and I put it into my phone, having done this I was prompted for an 'unlock code' ? Not having been given one with the new simm I phone support and asked for the code to unlock it. I was told to turn off my phone and restart it in 5 minutes and all would be well, no this did not work! I phoned back and explained the problem and was cut off! I phoned back again and spoke to another person who tried to help me with different codes but this was not working. The person said could I take the simm out of the phone and tell them the number on it, I did this which took about a minute and when I picked up my land line phone again the person had rung off. My view, I gave up and threw the phone away, as it happened it was an old phone and not really used at all, just as well I had another newer phone. The moral though, very poor customer service here, a shame full way to treat people, a sign of the times, oh dear!
Sounds like your old phone was network locked. As it worked with the old SIM I suspect this was EE as the old SIM was EE based. The new SIM cards are Virgin's own and present a different network number to the phone.
Ah yes that would explain it then, makes sense, I think that you are right it was an EE simm. It is a pity that these people at Virgin are not properly instructed in these issues. As I said in my original post the phone was old and so not a real problem, just as well by the sound of this. Many thanks for clearing this up for me though.