The answers are all in the source code, but since that's generally hard to read, here are some tips about Maemo Mapper and WMS servers (which is what your URL sort-of looks like).

Every WMS-based URL should have the string "SERVICE=WMS" (case-insensitive) in the URL format, at least in order Maemo Mapper to recognize it as WMS. I thought this was required of all WMS-based URLs, but your URL doesn't seem to have that string, even though it looks like a WMS URL ("GeoOgcWms1.3" is a give-away). So, you can add that parameter to the end of the URL (with an ampersand [&] before and/or after it, so that it doesn't screw up the previous contents of the URL), and Maemo Mapper will parse it as a WMS URL.

However, he coordinates ("BBOX=2581200,5683300,2581800,5683900") in your example don't look like latitude and longitude unless you insert a period into each of the numbers (presumably after the second digit?). Maemo Mapper expects decimal latitude and longitude numbers into the BBOX parameter, though, so it's not going to work if the WMS server expects some other format.

I'm not a WMS expert, so I don't know if it's illegal to omit the decimal point like that, but in any case, Maemo Mapper doesn't support that kind of omission, so it's unlikely that this website will be able to work with Maemo Mapper. :/

You can try emailing them to convince them to support WMS access in the more typical (valid?) way. If they're a good company, they might even listen to you. Good luck.