Can you describe your problem in detail?!?!?
"I have tried signing my MIDlet with my own certificate but device is still saying that it is untrusted." - What do you mean by own certificate?
But one thing to spot out is - Device should have root certificate for your code signing authority.
The procedure is I create a keystore using java keytool
Then I export the certificate from the keystore as test.cer file
After that I install that file on my device. It is shown among root certificates.
Then I sign the jar file with my keystore and try to install it on mobile device, but it still says untrusted source.
Any ideas?
Cheers