Foreign Networks

How about virtual mobile networks?
There are many virtual operators in addition to those above. These virtual mobile phone networks actually use the infrastructure of the big five. Here's a list:
 * Virgin Mobile use T-Mobile's network
 * Tesco Mobile use 02
 * Blyk use Orange
 * Vectone Mobile use T-Mobile
 * LycaMobile use Orange and 02, depending on certain factors
 * Talkmobile (The Carphone Warehouse) use Vodafone
 * BT Mobile use Vodafone
 * ASDA Mobile use Vodafone
 * abica use 3, Orange, and T-Mobile
 * Lebara Mobile use Vodafone's network
 * Giff Gaff use 02
 * Family Mobile (IKEA) use Tmobile

Follow the links for quick insights on the networks.