This list might be quite useful. It is a list comprising those Mobile Network Operator (MNO) or Mobile Virtual Network Operators (MVNO) who have SIM cards in the marketplace.

Please add to the list links for any MNO or MVNO SIM card from around the World. Please remember to identify in teh order [Country] [Brand name] and [Website] - thanks

UK Asda Mobile - www.asda-mobile.com
UK Asda- www.asda-phones.co.uk/
UK Family Mobile - www.familymobile.co.uk
UK Fresh (Carphone Warehouse) - www.freshmobile.co.uk/
UK Globalcell - www.globalcell.eu
UK Lebara - www.lebara-mobile.co.uk/en/
UK Lycamobile - www.lycamobile.co.uk/
UK 02 - www.02.co.uk
UK OneTel Mobile - www.onetel.co.uk/
UK Orange - www.orange.co.uk
UK Sainsbury’s - www.sainsburystelecom.co.uk/
UK Talkmobile- www.talkmobile.co.uk/
UK Tesco Mobile - www.tesco.com/mobilenetwork
UK Three - www.three.co.uk
UK T-Mobile - www.tmobile.co.uk
UK Virgin - www.virginmobile.com
UK Vodafone - www.vodafone.co.uk
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Institute for Digital Forensics (IDF) - www.linkedin.com/groups/2436720
Mobile Telephone Examination Board (MTEB) - www.linkedin.com/groups/141739
Universal Network Investigations - www.linkedin.com/groups/13536130
Mobile Telephone Evidence & Forensics trewmte.blogspot.com 

UK Blyk - www.blyk.co.uk/ (Although they've stopped operating in the UK, you still see their branded SIMs. They are apparently migrating all users to Orange.  

Trewmte would you mind if I replicated this list on my website?
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zibitdom.wordpress.com
www.zibitdatalab.co.uk 

- dngroen

Trewmte would you mind if I replicated this list on my website?

I have no objection dngroen, but you may want to pm Jamie.
_________________
Institute for Digital Forensics (IDF) - www.linkedin.com/groups/2436720
Mobile Telephone Examination Board (MTEB) - www.linkedin.com/groups/141739
Universal Network Investigations - www.linkedin.com/groups/13536130
Mobile Telephone Evidence & Forensics trewmte.blogspot.com 

And here from the Netherlands:

NL KPN KPN
NL T-Mobile T-Mobile
NL Vodafone Vodafone
NL Simyo Simyo
NL Lebara Mobile Lebara
NL Ben Ben
NL Lyca mobile Lyca Mobile
NL Tele2 mobiel tele2  

UK UK01 www.uk01.com They currently only operate in the Hewham area with trials elsewhere in London.
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zibitdom.wordpress.com
www.zibitdatalab.co.uk 

UK Vectone Mobile - www.vectonemobile.co.uk Interestingly from a look at the SIM card there are no forbidden PLMNs stored. The ICCID and IMSI point towards UK01 (Mapesbury Communications Ltd) though I'm assuming that it can roam onto any network as I do not believe that UK01 actually own any national infrastructure. I may of course be wrong with this belief.