In my previous window cleaning career I just changed my private house BT line to a business line. I paid a very little bit more every quarter but I got a free single line entry in yellow pages and also the business phone book.
I got asked to do a quote for a Gas showroom and a Meb showroom and in the end got 10 Abbey National, 2 Gas, 13 Powerhouse, 10 Coop supermarkets, various banks, building societies etc etc etc, all reasonably local and all from the same cleaning company.This was my main income for about 7 or 8 years.
Also I one day got a call from a Harvester who were desperate. That led to 3 Harvesters fortnightly. These jobs lasted for years as well.
I also picked up a Beefeater Restaurant fortnightly clean which I kept for about 5 years. Plus other jobs I can't remember.
Any of these calls justified the business line. It was from memory only about £5 or £10 extra per quarter. I don't think u need to spend loads on a big advert in yellow pages.