The upload and download speeds that can be reached with a GPRS and EDGE mobile phones depends on a number of factors. First, the capacity available in the cell. Usually, voice calls take precedence over GPRS traffic and in case not enough time slots are available for both, some GPRS timeslots are sacrificed for voice calls. Second, the capability of the mobile, or it's multislot class. Third, the network has to match the abilities of the mobile device. And fourth, the reception conditions experienced by the mobile.
The most comment GPRS/EDGE mobile station class today seems to be multislot class 10. Mobiles of this class can use 4 timeslots in downlink direction and 2 timeslots in uplink direction with a maximum number of 5 simultaneous timeslots. Depending on the amount of data to be transfered in the uplink the network will automatically configure the ongoing data stream for either 3+2 or 4+1 operation.
Some high end mobile, usually also supporting UMTS also support GPRS/EDGE multislot class 32. According to 3GPP TS 45.002 (Release 6), Table B.2, mobile stations of this class support 5 timeslots in downlink and 3 timeslots in uplink with a maximum number of 6 simultaneously used timeslots. If data traffic is concentrated in downlink direction the network will configure the connection for 5+1 operation. When more data is transferred in the uplink the network can at any time change the constellation to 4+2 or 3+3. Under the best reception conditions, i.e. when the best EDGE modulation and coding scheme can be used, 5 timeslots can carry a bandwidth of 5*59.2 kbit/s = 296 kbit/s. In uplink direction, 3 timeslots can carry a bandwidth of 3*59.2 kbit/s = 177.6 kbit/s.
While the numbers are quite impressive it should not be forgotten that a single carrier has 8 timeslots of which two are reserved for signaling on the first carrier. Using 6 timeslots for a single mobile means almost the complete carrier is used for the data transfer of a single mobile. Under realistic conditions it's unlikely a cell has that much free capacity to offer next to voice calls.