Google Adwords is better value, but you need to have a website.
Its pay-per-click advertising that you can set the price you're willing to pay for each click, highest bidders get shown.
You can set your monthly spend limits. The returns for commercial work is far greater than Yell.
This is a good way to get your company seen regularly, at least until you get your fist page ranking on free Google.
We were spending £200 per month on Adwords (we set that limit) and achieved at least £500 p/m return.
Stopped using it now cos we managed to get a first page listing on the natural listings which is free.
With Yell you got a lot more domestics. Everyone one in commercials sits in front of a pc all day so generally look for services by searching Google.