Got my 32gb black one yesterday. My uni held it for 3 hours before they would let me collect it from the parcels desk. Those 3 hours dragged so bad because I knew from parcel force that it had been delivered.
The main reason that the blade is rebooting now is because it is getting a little old now so driver support is limited but also some games/apps that are intensive will cause the phone to force reboot. You will be experiencing more force reboots on ICS and JB roms because they are still not yet stable.
What happens if you put this sim in a different phone. Have you tried contacting Virgin Mobile about this (though i suspect, like all mobile operators, they will be less helpful than a chocolate tea pot)
I would have a look at either the Huawei Ascend G300 or a ZTE Blade III. The G300 already has a large community on MoDaCo. Currently it is easiest to get one from Vodafone and get an unlock code from eBay but Tesco and Asda have sold them in the past too.
The blade 3 is a bit of an unknown in the UK at the moment so if you want something you can take out of the box and hack straight away go for the G300 but bear it in mind that the G300 will be superceeded soon by the G330.
I have bought a phone (one of the many ill-fated ATRIXs that I've had) from CeX and it arrived out of the box with an unlocked boot loader, custom ROM and root. I don't think that they really check for that stuff too much, so long as it looks like it's stock then they don't seem to notice but then that is just my experience with them.
Also as a word of advice, I am still dealing with them regarding the replacement of the atrixes with my Xperia T, I'd get cash and buy something elsewhere with it, my experience of their online customer service is diabolical, it has taken them 4 months to replace a phone that broke within it's warranty period.