A channelized T1 contains 24 individual DS0 channels, each capable of carrying voice or data. The full set of channels has the same speed as a full T1, but the individual channels may be split into voice lines or data lines using a device called a Channel Service Unit/Data Service Unit or CSU/DSU. The CSU/DSU allows the voice channels to be connected to a phone system or PBX. The data lines are then connected to a router serial interface and often are used to provide Internet connectivity.
Good job on explaining the channelized T1. I would add that a channelized E1 is the European version and varies slightly as it has 31 DSO's. 30 bearer channels and 1 D channel. The channelized T1 has 23 bearer channels and 1 D channel. These are the Primary Rate Interfaces (PRI) in ISDN services.