well they don't xray you bag when you go into the phil so I doubt they enforce it.
I usually carry 3 phones.. 6 is a lot if you get questioned - I'd bet you'd be ok with four.

BTW there are plenty of free tools (online or a download) that will unlock your phone for free I have used this http://unlock.nokiafree.org/ to unlock my nokia :sport-smiley-003: thus saving 5quid.