(keitai-l) Handling the various Carriers and Models

I am starting to explore mobile web application development, and was
wondering about the common ways companies in Japan deal with the various
formats (cHTML, XHTML, etc.), and models (SO505is, SO504i, etc.) in the
context of delivering content/web application. Some methods that I run
across are different URLs, and auto detection, but I wonder what other
strategies/examples are out there.

Different URL:
I see on advertisements that some companies use different subdomains or
subdirectories for each carrier to deal with this issue (ie. i.sitename.jp,
v.sitename.jp, sitename.jp/i) . I guess they don't have to worry about a
single site that does it all. I imagine the drawback is they have to worry
about three different versions, and within those versions deal with models.
Sounds like this would be a better approach when dealing with sessions.

Auto detection:
I've read through a past post titled "Max HTML sizes on keitai", and now
understand that from the HTTP headers you can pull the carrier, model, and
cache size. I guess that you could create an engine that uses this to serve
the appropriate data. Are these types of engines common? I ran across an ASP
service, and an IIS server component called KARAKURI. What other
products/services are out there? Or is it common to create your own?

Thanks,
Chris Kobayashi
NewB mobile web app developer ...