O2 UK to block unlegit iPhone from its network?

UPDATE 12/NOV/2007:
Works fine, no worries then.

UPDATE 09/NOV/2007:
10am: works fine still.

ORIGINAL POST:

Third degree rumor! Through a friend I’ve heard from a source within O2 that they intend to run online checks on their network to decline those iPhones the use of the network that have not been properly activated and registered with O2 in the UK but self-activated, hacked and maybe unlocked.
This would use an IMEI check, since this is transmitted when a device attempts to book onto a GSM network, the MNO could allow or disallow access. As you know the IMEI contains, manufacturing country code, manufacturer code, product specific code and unique identifier. The same system is used to prevent stolen devices to access a network.

Now, would the solution to this issue not be a simple IMEI hack I wonder? Spoofing a different IMEI (non-iPhone) should successfully trick the network into allowing the device by bypassing the recognition as an iPhone.
I can give an update on this over the weekend when we had some chance after the official launch to see whether there is substance to this rumor or not.