Hi there, Kmmcab:
I would just like to offer one suggestion that hasn't been mentioned yet.
It seems that the best way to get links (and publicity) is to have something SPECIAL about your business. In short, you need to be able to answer the question:
"Why should people use our cab company instead of our competitors?"
If you have a simple answer to that, then you have to promote that answer.
If you don't have an answer to that, then you had better find one.
For example, there is Ben Franklin Plumbing, which is known as "The Punctual Plumber." Their answer is, "people should use us instead of our competitors because we show up on time."
So what can you do that your competitors can't (or won't)do?