Need to understand your question better. You are migrating the legacy PBX with Analog phones into IP PBX (CME system), and you would like to know what are the options on CME to support more than 4 analog phones? If this is the case,
- You need to know the CME platform capacities (Every analog phones will utilize a phone user count. on 2851, the maximum number of phones supported is 100, and on 3845, it is 250)
- You will also need to have VG224 to be the interface between the CME and the analog phones when the analog phones can't attach to the CME router directly. A single VG224 can connect 24 analog phones and it will convert the FXS to SCCP to allow CME control those analog phones as Skinny IP phones.
If this is not the case, can you elaborate "numbering scheme for various campuses to come up with FXS and T1 ports to support legacy systems"? 2851 is acting as GW to interact with Legacy PBX?