cheapest phone company for small business

Has anyone changed over from eircom to another provider and found them cheaper. At the moment I am diverting all my calls from office phone to my mobile but I am paying twice the price for each call. Even when I am in the office I leave the phone with this setting because it costs just as much to change setting each time. I never use office phone for anything else yet my average phone bill is 150 euro a month with eircom plus an average of 200 per month on mobile calls with vodafone. There must be a cheaper way of doing this.
I have thought of an answering machine but I think some people just hang up when they get an answering machine and also it shows that office is unattended. Any ideas???

Hi Celtic, You could try using a service like www.mydivert.com
You would be able to get a virtual number and still route it through to your mobile. You will still incur charges but at a much lower rate than eircom, the only problm is you would have to change your phone numbr which might mean costs incured for redoing stationery etc.