I was originally posting on the large 'New Sim issues thread, but as that has been shut down, I'll post an update here. My old phone was a Nokia 6303 on PAYG
Finally received the FOC replacement phone on Wednesday - no prior notification of delivery time / date from either Virgin or Courier Company. The phone arrived in a flimsy card box in a doubled over plastic bag - no other packaging at all. Having read previous posts re mobile data charging, I set up a link to home wifi before putting the Sim in. The 'manual' that comes with the phone (Mobiwire Oneida) is minimal to say the least- more comprehensive instructions were found on the Vodaphone website. The first thing that the phone showed was that it needed a software update, which completed over home wifi. Once that completed, the new sim was inserted & mobile data turned off.
Note that mobile data cannot be switched off until the sim is put into the phone, so if no home wifi is available, then charges may be incurred for the software update. I suspect that alot of users of the older phones on PAYG will not have wifi at home - another part of this whole sim swap that hasn't been thought through.
The new sim worked immediately , and has continued to do so since. Yesterday I even had a call from Virgin Customer services to check that everything was OK !.