Blackberry Bold 9900 (blocked maybe) ?

Blackberry Bold 9900, i bought this phone and did work the guy said it was on tesco, i put a o2 sim in it also and that worked fine aswell as a tesco sim, the next time i switched the phone on it says at the top no " phone not allowed mm6" so i persum this phone has been blocked< in the right hands im sure this is usefull to someone it may not even be blocked. comes with charger and the phone itself is in good cosmetic condition with no visible scratches to the screen