Using the iphone phonecall keyboard

[walkman1943]

Hi Folks Recently I was making a call via my iphone4s to my bank. At the beginning of the call I was asked to enter my postcode as a security answer. I tried using the letters on the phonecall keyboard without success. I expected that if I pressed the 2 a couple of times for example I would get the choice of a capital or a small a but nothing happened. I googled this & also looked in the 4s user guide but no success. I'm using IOS 6. Thanks for any help you can offer about this problem. Regards Gerald