The reach of DDD was limited due to the inefficiency and expense of switching equipment, and the limited ability to process records of completed calls. An early obstacle was that the majority of switching systems did not provide Automatic Number Identification (ANI). Common control switches, such as the 1XB switch, were fairly quickly retrofitted to provide ANI, and most 5XB switches were initially installed with ANI services. Panel switch were eventually retrofitted, as were some step-by-step systems that were not scheduled for immediate replacement. Even if a switch had ANI, it could not identify callers on party lines. This was only partly overcome by tip-party identification for two-party lines. As the cost of subscriber line carrier declined, party lines were gradually phased out.