Cuts of in the middle of calls

I have had the BT Freestyle 2200 for about 4 years with no problems but recently it has started cutting off in the middle of calls and sometimes before it has even finished dialling the number

When in it does this a series of horizontal lines appear on the screen before it goes back to normal, showing full battery and that it is in range.

I have recently got BT wireless broadban but even when I unplug all of that the phone is still faulty.

Thanks for you help