Sorry if this has been covered before, but I have just found out how EE currently deal with replacement SIM cards. I bought an iphone 5s to replace an ancient iphone 3gs, so needed to get a nano SIM, contacted EE on-line selected the correct options, ie a replacement SIM of a different type required due to replacing current iphone. No bother, "we will send you a TXT when we have dispatched the SIM and then you follow the link provided here "newsim" ).  Got a TXT on Tuesday afternoon to say SIM will arrive in 3>5 days - great!  The post arrived at 12:00 today as we were leaving to go out, SIM card was delivered, checked phone when we were out of the house - "no service" - very strange. Anyway, to cut to the chase, currently, despite what their website says, EE activate the new SIM roughly 18 hours after they despatch it - of course this disables the previous SIM which is at that time still being used!  When questioned about this the EE said this is how they do things to make it easier for you - blurb on website points out that for security reasons, they only send you an activation PIN after you have proved that it is you that have received the SIM - no they don't! So, take care as to where you are if you are changing SIMs, as you might just lose your ability to use your phone. Checking on their website, quite a few people have been reporting "loss of service" while waiting for a new SIM.

Edited 18 November, 201510 yr by rum4mo

EE/Orange/Tmobile have always done this, and it's pretty much standard practice with all the networks.

When I had a replacement sim from EE, as soon as it was used it automatically killed the old sim.

Best bet next time is do it in store as it's instant.

Just done this myself moving from 3G to a 4G sim.

When it arrived it had a temporary number and approx an hour after inserting it, EE systems had moved my number across to the new card.

Not sure what happened in your case Mo

Mrs Goldfinger has just gone to a 4G Sim only deal with EE, , previously with Orange (3G), new sim arrived, old sim out, new sim in, worked instantly, no break in service.