My phone has a fast busy tone.

Try these steps first to narrow down the source of the issue:

1. If you are using a cordless phone, disconnect all cordless phones from phone jacks. If you have a corded phone, try it in the same jack. Sometimes, cordless phones are more susceptible to interference.
2. If you cannot check the connection with a corded phone, unplug the cordless phone from the power supply for at least 15 seconds and try again.