Who hosts the site for you at the moment? Do they offer a mobile optimised option?
I don't know what kind of site it is, but if you are getting a lot of mobile traffic it might be worth looking at moving to something like Squarespace, or if it is a very simple site, maybe Wordpress? I'm sure squarespace do native support for just about all mobile devices, and wordpress automatically present the mobile version to me when I'm on my phone.
It's kind of going to depend on what the site does, and how much knowledge you have (or cash/time, if you don't have much). Getting the site optimised shouldn't be hugely expensive and there will be reputable firms, but you will need to look carefully.
It depends a bit on what information you want to make available on the mobile version and why, plus whether you have the techy skills yourself to make html pages (or someone you can pay a smallish amount, rather than a mega 'design' package)
But if the mobile sector is important to you, becasue it is relevant to your business, then you may need to invest in something 'nicer' to get the custom.
The pages which display on a mobile are just html pages, not technically difficult, but it's a question of thinking what info you need to get across and putting it in a way which is uncluttered.
Thanks for replirs. It's a very large site, on zoomla and hosted by bt but built by me. As a temporary measure, I have now put some links to mobile friendly pages whhere I ve done simple pages with large text, while I look at the options. Thanks.