What carrier/handset are you using?
In general a "trusted application" is probably one that is signed with a digital key granted from the carrier. You need to approach the carrier, tell them you want to publish your own MIDlet, ask for an identity certificate, and pay them boatloads of cash.
They will probably ignore your request but if you are a real player and have real money, they may give you a long
string of random looking digits that you can include in your JAD properties that verifies the application comes from a trusted (i.e. paying) partner.
Good luck,
William Frantz
http://SprintDevelopers.com