Take an example for a hotel has 200 rooms, with 10 DID line and 30 DOD lines.
The originating traffic rate & the terminating traffic rate for a hotel is much difference from residential subscriber line.
For normal residential subscriber line, the originating traffic will be only 0.04 to 0.05 erlang. But for business line is quite different, it will be 0.06 to 0.16 and depend the type of business line you have.
You can divide the rooms into say 5 trunk groups, with room no. 1,6,11,16… to be TG 1; room no. 2,7,12,17…. to be TG 2, room no. 3, 8, 13, 18….to be TG 3 and so on….. Each TG will have 5 DODs, the other DOD lines will be used by office.
You also can plan the overflow routes between the TGs. Suppose TG1 overflow to TG3 and then overflow to TG5.
It is only a simple configuration for such small size phone lines.
(The traffic rates of residential lines had been already mentioned above. You also need to know the day to busy hour ratio, there should be have two different busy hour for residential lines, and the day to busy hour ratio will be 10 to 12)