Non geographic numbers

We are new to the travel industry, and having spent the last 25 years running a successful telecommunications business it amazes me to see how many companies still advertise their main telephone no as an 0870 or 0845 number when most people nowadays realize the extortianate cost of calls to these numbers when compared to an 0800 freephone number.
The number of incoming calls from a marketing campaign would increase dramatically when choosing the latter.