Unfortunately, some times, time is the big restriction. Do you remember that task involving LaRedoute?
They had full internet access. However, they chose to not research LaRedoute and basically went in to the pitch having done zero research.
To not offer full internet access (especially when they have smart phones, as well), seems like handicapping them for no reason.
Yellow pages vs internet: yellow pages lists many numbers, all in a row. This allows a person to make call after call, very quickly. Doing an internet search will be slower and might be the reason why they prefer to use a phone directory, rather than the internet when making multiple phone calls.