At lunchtime today I walked to the nearest Carphone Warehouse and walked out with a Galaxy Tab for £499 (with a 1 month rolling contract so I can decide what do to longer term). I verified that it is indeed not SIM locked: they had a stock level of precisely 1 so it was the same Tab whichever network I chose.

The sales guy was a bit green about the gills: he was waiting for an excuse to open the box, and he plans to buy one provided he can get his girlfriend's permission (or possibly even without).

No chance to play with it yet as I'm at work, but according to the box it includes a free 16GB microSD, so that might be useful info for anyone else ordering one: you may not need to buy a separate memory card.