I can tell my users that if they want wap content they should go to wap.domain.com but what if they donīt remember this and they access www.domain.com? The logical thing would be to try to convert those guys into sales serving them wap content through cloaking. And, of course, cloaking is something I still want to avoid. So, could someone tell me how you solve this issue?
This type of cloaking is common and not a problem for seo purposes. What you want to avoid is showing one version of your site to search engines but another version to real visitors who use a web browser to access.
For example, googlebot and an engineer at google using his desktop computer should see the same thing.
I wouldn't keep wap.domain.com - just show different content. More user friendly - your visitors don't have to remember multiple domains for your site.
Think about it this way: Your user is sitting on the toilet (where I think 90% of mobile surfing is done) and painfully types your domain into their browser with some horrible t9 interface. Make it simple for them - just let them type in your standard domain. Don't make them guess what the mobile domain might be.
On a related note - is anyone coding in WAP anymore?
Most phones can display html - I would think a stripped down html page is fine for most mobile users. You may even just be able to change stylesheets and have all your content mobile friendly.