
Yes, reading my thread back, I suppose it's a bit muddy! 
1. I don't dial 1899 before my call, I have to dial
08081 708 708 first (because I'm on ntl).
2. Because this is a bit long-winded, I had pre-programmed this number into the memory on my phone.
So, I press memory 8 before I make a call.
3.  This used to work fine, when I then pressed another memory-stored number on my phone, eg memory 1.   (Therefore at this stage I have pressed 
memory 8 and memory 1).
4.  The sequence seems to have recently changed, as the instructions now are that I have to finally press the hash symbol on the phone to be connected.  
5.  My phone doesn't like this as a voice then says that the number I've rung (memory 1), has not been recognised.  (Yes, I have checked my memory 1 etc and found it to be correct).
6. When I redial using the full telephone number for the memory 1 number, I can get through ok.  This is the same for all my other memory-stored numbers.
This is a real pain!
I hope this explains my problem better.