The number of EDGE subscribers sharing a PDCH slot is the same as for GPRS. This is a parameter which you should set. The limitation is maximum 16MS in downlink, maximum 7 in uplink (3 bits 0-7; 0 is reserved), but the sum is max 16 as on PTCCH/D the timing advance for up to 16 MS could be transmited. Note that some vendors does not support GPRS and EDGE on the same time on one and the same timeslot.