"Try the test socket says the service provider"!!......
If your dialing tone starts to sound like the engaged tone & you can make & receive calls OK the most probable cause is a messenging service, eg, BT 1571 (& no amount of trying the "test socket" as your call provider will request will fix it!!!!).
What is BT Answer 1571?BT Answer 1571 is an answering service that answers calls when you're away from the phone or engaged on another call. You'll know you have a message in your mailbox if you get an interrupted dial tone. This service also includes the following features:
- Record your own personal greeting for callers to hear, changing it as often as you like
- Stores up to 20 messages
- Messages stored for 60 days or 20 days if you've listened to them
- Access your messages when you're away from home. All you need to do is set a PIN by choosing option 3 on the 1571 menu. Then to check your messages when you're out and about, just dial your home numb...