VoIP - ISP's Need To Improve for Small Businesses To take up

I'm a manager in a small UK company whose portfolio also includes looking after the company's computers and telecommunications. On a daily basis I am contacted by telecom firms asking me if they can take 'just 10 minutes of my time to save me 60% on my phone bills or similar'. Now these guys are not selling VoIP but something called carrier pre-select. That's when you pay your line rental to one company and pay for your call charges to another, who will charge you at a lower rate than the line rental company. I have to say these guys are seasoned telesales people. They know every trick in the book to keep you talking, a few haven't even got the hint from my standard line of 'I need to finish this conversation now and hang up the phone'. Anyway to get me a better line to tell these guy's I'd love to be able to say 'we