iHold A4LP 4-Line Music On Hold Player system for all corded or cordless 2 line or 4 line telephones, "All-In-One" Music On Hold adapter plus mp3 On-Hold Music Player Works with 2 line or 4 line Corded or Cordless phones and PBX phones Pre-loaded USB flash dirve included, SD slot provided Flash then Hold Activation on any 2-4 line telephone Hold Activation on any PBX telephone or many compatible 2-4 line phones