Multi-Account SIM cards

The website of NOWGSM is about as bad as it gets… but they do sell the very-clever-if-it-works Super Sim 16-in-1 device.
A lot of photographers who travel a lot end up with a load of local pre-paid / pay-as-you-go SIM cards for different countries. This device should let you clone up to 16 different SIM cards onto their one special SIM card, and then you can switch between the different accounts. It appears, at least from the picture there, that if you have a smartphone like the SonyEricsson P910 (or maybe others too) then you can switch between lines via a menu.
Note that it doesn’t work on all SIM cards, and may be illegal in some countries.