sim cards (interchangeable)

is this how it works...
i bought a pay monthly plan, that came with a sim card and a phone, and an extra (PAYG) sim card.  Can I buy a used phone (from same network {or unlocked} ) and use my pay-monthly sim card on the used phone, and the payg-sim card on the phone that came included with the monthly plan...  Basically phones and sim cards are not one-to-one, but I can take my sim card with a monthly plan to go on any other phone I want, just as I would with the payg sim cards?
...just checking...

 

I'm pretty sure you can put any sim card in any phone you want, as long as it's unlocked or the same carrier. My boyfriend just put a US pay as you go sim into his UK phone (which is also pay and go) with no issues.

My phone was a Virgin locked phone w/Sim (PAYG), I then got a used phone that had been an old O₂ contract phone and was able to put my Virgin Sim card in it and use it no problems. But then I switched to O₂ Sim (better deal cause hubby is on that carrier) and then my phone became possessed and randomly started calling people so I took my Virgin phone in and had it unlocked for £5 and put my O₂ Sim Card in and am having no problems at all.

Simple answer: yes.

You can use your sim in any phone that is on the same network or unlocked. 

Some networks like Virgin piggyback off others (like T-mobile), so you don't need to unlock either handset if you're using either network's sims.     Just a hint to save some cash.

Some networks like Virgin piggyback off others (like T-mobile), so you don't need to unlock either handset if you're using either network's sims.    Just a hint to save some cash.

Does this work?  Even though they share infrastructure the virtual networks have their own MNC and I thought that was how the software checked.

Does this work?  Even though they share infrastructure the virtual networks have their own MNC and I thought that was how the software checked.

Virgin piggyback's off T-Mobile.  I used to be on contract with Virgin, then moved to T-Mobile.  I hate the phone T-mobile gave me, so went back to my handset from Virgin.  Have had no problems going around the country with it.     Never had it unlocked.  Tried my old Virgin SIM in the T-mobile handset same: no issue between them. 

Some networks like Virgin piggyback off others (like T-mobile)

A large number of "networks" are actually just subcontracted to another.  Until a couple of years ago there were only four physical GSM networks in Britain:  Vodafone, O2 (originally Cellnet, now owned by Telefonica), Orange, and T-Mobile (which started out as Mercury's One2One).   There are another four fledgling networks which have opened up very recently, which you can see here:

http://www.gsmworld.com/roaming/gsminfo/cou_gb.shtml

Anything else which purports to be a "network" is actually operating over one of those physical networks listed.

Does this work?  Even though they share infrastructure the virtual networks have their own MNC and I thought that was how the software checked.

Some virtual networks have their own MNC, but not all.  The current list of allocated codes can be seen here:

http://www.ofcom.org.uk/telecoms/ioi/numbers/numbers_administered/mnc.xls

When I had my Virgin PAYG phone unlocked to use my O₂ PAYG Sim card I asked about my old Motorola O₂ phone. The tech explained to me that the Motorola phone was an O₂ contract phone and that with many contract phones because you end up paying the contract regardless you can often just pop a different company Sim card in it. Which explained why both my O₂ and Virgin Sim cards worked in the Motorola which had never been unlocked.