Phone rings oncce and cuts off - BT Synergy 6500 Cordless Phone - DECT - Silver Titanium 1 x Phone Line - Answering Machine - Caller ID - Speakerphone - Backlight

you're gonna need to go to your menu options to change the number of rings. Google your model and then look under manual. Perhaps this is it: http://www.home-phones.co.uk/assets/uploaded/documents/384_BT_Synergy_5500_userguide.pdf

The instructions say you change them using the answer phone menu in the base - you need to scroll to 'answer delay' and you can increase the rings to a maximum of 8

You must get the phone unlocked from the service provider who gave you the phone. So call up the service provider to get the unlocking code so that oncce unlocked the phone will work any where.
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if you dont have garanty format

When the ring tone cuts out, your caller goes to your voice mail, right?

The length of time before an unanswered caller goes to voice mail is called your "ring cycle" and is set by your phone carrier (e.g. Vodaphone, Verizon, Orange, etc.)

There shouldn't be any charge to change your ring cycle, and some cell carriers will let you adjust it from your account settings on their website, but the simplest answer is just to call your carrier's customer service and ask them to change the ring cycle for your number.

For cell carriers in the US, you can call 611 from your phone to reach your carrier's customer service, but I don't know about other countries' mobile carriers.

if answering machine is on phone , go to messaging menu it should have a setting for number of rings... make sure toll saver option is off!

It is very possible the engine oncce had a oil heater for cold climates.

This is controled by your mobile phone provider. not an phone issue

just set the amount of rings higher on the back of the phone and make sure all you old messages are deleted and also make sure its not set to do not disturb

sorry but oncce they get wet they never work the same again
It may come to life if you leave it dry a little while longer but the damage is done
You will find if it starts to work again that all sorts of faults will occur as time goes bye