Hi Vikas,
if you have 4/4/4 config, then supposing each cell has 1 SDCCH and SACH,FACH etc leaving 4TS free on BCCH and other trx have 8ts, then 8*3+4=28, the for 3 cells it becomes 28*3=84 calls. so at max 84 tch can be configured at Full rate so 84 subscribers but you may have to increase the SD count if its a busy site. i have not considered any pdtch configured on site