Front end designed for mobile devices
If you have a traditional website like ours, that doesn't resize to the correct screen size, you can create a mobile friendly mini site that is separate from your main site. We introduced ours a few months ago.
For us, 80% of our users want signs and symptoms information, which accounts for 20% of our site content. So our mobile pages are focussed around this key journey for visitors. Our site has 2,000 pages, our mobile site has about 80 core content pages. This is one of the cheapest ways to starting offering an improved user experience.
In my opinion this is a stop gap, as the user experience is sub standard. As it's a mini site, not all your users will receive the information they are looking for, unless they jump to the desktop site.
With this extra mobile site on top of your normal site, you have more content to update and manage.
Making your current site more mobile friendly
There is a really cheap way of improving your site for mobiles. And that's using bigger buttons and larger clickable areas. Try clicking text links with your thumbs. it's very tricky.
With our current site, we're using large sign posts to help people click and go. With the BBC they use larger clickable areas as well.
This is a great no cost option, but the effectiveness of this approach will obviously depend on your site design.