There are different types of CallerID available from the telephone companies. What services do I need to use MOH?
For the purposes of this document, we will use Telco terms that are used in the United States. These services may be called by a different name in other countries. First and foremost, you must have Call Waiting in order to take advantage of MOH. CallerID (CID) is not required. There are 2 types of CID, type 1 and type 2.