There is no limit regarding the amount of personal recording aliases you can have, however there is a limit of how many aliases you can have total on the TCS if using H323. This is dependent on the registration mode you're running on the TCS, either terminal or gateway. If using terminal mode, the maximum number of registrations allowed to the gatekeeper is 25, but if using gateway mode, there is no maximum.
It's not mentioned what the maximum is if using SIP, but it might be safe to assume that if you register to a gatekeeper using SIP the maximum number of 25 would apply, and if using a SIP trunk, there would be no maximum. Using a SIP Trunk was introduced in TCS S6.2 software.
Refer to the "Site Settings" section of the TCS Admin Guides that is specific to your TCS version for more information.
