Yes, in B10, you can mix. You can’t in B9 ? I thought you could.
Since your BCCH is already PGSM, you don’t need a second TRX with pure PGSM frequencies. The amount of old MS must be very small.
There is an indicator that can give you the ratio of EGSM MS in your network (I’ll give you the name tomorrow… but you can find it in RNO by searching “EGSM” :)) )
Just one question : why do you need more than 42 BCCH freq ?? Is your network design really terrible ? The amount of interference is that bad ??