I'm helping a client set up a mini mobile friendly site, it's just a few pages with an overview of what he does, how he does it and contact details - basically a summary of his much larger regular site.

To give the visitor a choice of visiting the mobile site, there seem to be a few alternatives but all seems to have their pitfalls. I'll outline them here and maybe I can get some feedback from people who have done something similar.

Detect and redirect
I can add some code to detect the phone user and automatically redirect them to the mobile site. Problem here is that the user may actually want to visit the main site.

Detect and ask
Detect the user and then for this session only have a pop-up asking if they want to visit the mobile site. That's ok but I'm not overly keen on pop-ups.

Detect and show a link
If the user comes to the site a link appears in the top nav bar that they can click to go to the mobile site. Problem here may be the link would be missed as it would probably be quite small. There may also be worries about hiding the link for regular users / search engines.

Just add a link
No detection, just a link on all pages to the mobile site. Problem again is the link may easily be missed and regular users clicking on it and not realizing the formatting is optimized for small screen sizes.

What approach would you go for here?