Faisal prepared a nice tutorial explaining how to enable people to download SIS installers on your web site when you do not have access to chance MIME types manually. He provides examples on PHP and ASP.Net, and covers S60 1st, 2nd and 3rd editions, which should cover all cases out there.
In this article I will try to explain you how you can enable OTA (Over The Air) installation of SIS files from your own websites without any settings on server. Enabling OTA installs require you to set the correct MIME-Type on the server, so the mobile browser can recognize what kind of data server is returning and install the SIS correctly. You can manually set the the MIME-Type as described below on your webserver, however this article targets when you don’t have access to server settings for custom MIME-Types