darkroomsource,
A frozen ATPL is simply a CPL/IR and MCC. It is not an actual licence, just a name given to describe this particular stage in your training, and therefore the bare minimum to be deemed recruitable as a First Officer by airlines in Europe.
The ATPL becomes 'un-frozen' when you achieve 1500 Hrs, 100 night hours, 500 multi-crew hours and several other factors, including having passed an ATPL skills test (usually in conjuction with an LPC/OPC in the sim).
Hope that's helpful.
Regards, SF.