Phone restriction Off - 8310 - T-Mobile

If you put an unlock code into an 8310 locked on a T-Mobile it displays
'Phone restriction Off' message but what does that mean exactly. I only ask
because the 8310 still will not accept an O2 or an Orange Sim. Both the
later are more modern sims with dif amount of contacts on them. Could this
be the reason why?
What does Phone Restriction Off mean if it's not a multi network lock
release?

TIA
Andy