Indirect Access is simply a method of routing your telephone calls via another carrier than the supplier of the lines. Openreach (a BT company) maintain the lines we supply to you. The method of access to route the call over the another carrier may be via CPS or Indirect Access. The difference between IDA and CPS is that CPS places the routing instruction at the BT exchange (the local exchange is programmed to route some or all calls over a single, pre-chosen, carrier).

IDA can be a manual or an automated process. Automation is usually done via a telephone system located at the business premises. Historically, this was also done by either placing pre-programmed hardware between a telephone, or telephone system, and the BT point or via programming the telephone system. CPS has generally replaced these methods when it was introduced several years ago, but programming a telephone system can still help in routing certain call destinations over specific carriers.