Digitally signing a J2ME application so that it runs in Operator domain

[O S]

We are supplying a J2ME (Java) application to a mobile network
operator. We need it to be digitally signed so that it runs in the
Operator domain (as opposed to the Trusted Third Party, Manufacturer
or Untrusted domains). Can someone tell me the process for doing
this?

If there is a seperate process for each phone manufacturer, has anyone
gone through this process with Motorola, SonyEricsson or Nokia? What
are the details?

If the mobile operator needs to perform the process, that is fine, but
I still need to understand what they need to do.

Thanks.