Plug the telephone into other phone jacks in your house to see if the short is in just the phone jack you were using. If the problem persists then you can be assured it’s beyond the single connection. Locate the exterior test box where the line from the telephone connects to your house.

An open circuit implies that the two terminals are points are externally disconnected, which is equivalent to a resistance R=∞ . This means that zero current can flow between the two terminals, regardless of any voltage difference.

An open circuit is a circuit where the path has been interrupted or “opened” at some point so that current will not flow. An open circuit is also called an incomplete circuit.

To isolate the problem:

1. Hang up all your phones. Be sure they’re all hung up completely. If any were off the hook, wait a moment, and see if this corrects the problem.
2. Unplug equipment and test jack. Unplug all your equipment. First, unplug your phones from both their jacks and electrical outlets.

Make sure the phone cord is plugged into the correct port on your phone or device. Unplug the phone or device from the wall jack. Plug your phone or device into another wall jack that you know is working. If the dial tone returns it means the previous wall jack is damaged or defective.

If you have no dial tone on your corded phone, make sure it is plugged securely into the wall phone jack. If you have no dial tone on your cordless phone, check the battery and charge it if it’s low. Make sure your cordless phone’s base unit is plugged into a working electrical outlet.

Test a corded phone

1. Unplug the phone from the wall jack.
2. Plug a different working phone into the jack.
3. Check to see if you still hear static or don’t hear a dial tone.
4. If the problem goes away, repair or replace the phone you just unplugged from the wall jack.

The idle handset will display NO LINE if it does not detect a live telephone line. Check the telephone line connection both at the phone jack and the base. You may have a defective telephone cord. Try replacing cord between the jack and telephone base.

Re: Phone says””line in use” When a phone on the line is off hook the voltage drops way down triggering the indicator. If you are getting this indication when all phones are on hook, it indicates a bad phone or a bad Telo.

The “NO AC” display is a diagnostic message telling you that the controller has stopped receiving AC power. The controller is running on the power supplied by the backup battery. Check the power source by plugging a lamp or radio into the wall outlet to verify there is power at the outlet.

A multimeter is used to test a phone line without a phone. If multimeter functions properly then the reading will appear on its digital screen and this will emit a beeping sound. Continue the test to all the phone lines.

Using Busy Call Return and Last Call Return

1. After hearing a busy signal, if you want to be notified when the line is free, dial *66.
2. To cancel the busy call return request, dial *86.
3. To hear the phone number of the last incoming caller, dial *69.
4. To cancel the last call return request, dial *89.

Get Even More Info on Call Forwarding: *#61# On my Galaxy phone, this code prompted a pop-up that let me know how long until a call is forwarded to the message center.

If you can hear the ringing sound at the starting followed by busy tone that means the person is speaking to someone else or is trying to call someone at the same time you’re calling. And if you’re getting busy tone continuously then they may put the mobile in DND mode.

So if you mean undivert forwarding from your phone so that you will receive calls from the caller (i.e. the phone call being forwarded to another number than your own), you can check for and remove the call forwarding setting on your phone. A similar setting can be done/undone on Android phones.