I don't bother, but I fall into more or less the home installation (small home office, just me) category.
Instead, I have rules that allow me to dial most numbers as-is.
So, anything eight digits long is considered a local (London) number and gets automatically prefixes with 020.
Anything six digits is considered local to my home town (Winchester) and is prefixed 01962
Anything four digits is an extension at my major client, so gets their DDI prefix added
Anything three digits long, or starting 118, or 141 is a British Telecom short code, so goes via PSTN
Anything two digits long is an extension, so I can phone myself in another room, if I want the exercise running to answer it.
NIgel