Here is some data from the Nielson group on smartphone penetration:

For The Young, Smartphones No Longer A Luxury Item

If you look at the 18-24 year old segment, 56% of those surveyed own a smartphone.  So, if we can extrapolate out, that is quite a wave of mobile traffic coming to your website.  Your customers may not be using mobile devices to access your sites today, but this indicates that things are changing fast.  Within the next 5 years, most websites will need to be designed for mobile, OR have a second site aimed at mobile users.

One thing I do think is that many sites can be adapted to display reasonably well on a mobile device.  So maybe that’s the play to make – otherwise you’ll be maintaining 2 sites, and compromising your content layout and structure.