Can we distribute our Symbian Application files .sys files via. OTA as we can distribute the MIDP applications. If yes can anybody tell me about how to set up the MIME types for that & what all is involved in that process.
It is possible. However, if you are doing WAP download, you should know that there can be different size limits in the WAP gateways.
Read a posting on the General Symbian Platform Development board:
http://nkn.forum.nokia.com/devrel/threadshow.cfm?mb=5061606466647644&msg=8644371895327175&page=1
SIS file is already recognized MIME type in the Symbian. You can also define own MIME types. Read about Recognizers from the SDK Help.