Always getting number unavailable with Cisco dial plan

Dial plans are fairly easy to read but there is one little gotcha if you enter in one of these incorrectly: you will always get number unavailable.

You need to make sure that the dial plan you have entered in is valid i.e. it uses the | pipebar for delimiters and has no spurious close brackets ‘)’

The web interlace of a Cisco IP phone does not validate your input.