Java Midlet Certificate

We are developing java midlets for mobile phones using only MIDP 1.0 and WMA. The midlets need to be signed, and so far we have successfully managed to get signed versions running on LG U8120, Nokia 6600, Nokia 5140 and Nokia 6230 (with a Verisign Class 3 Java Object Signing 2004 CA SHA1withRSA certificate). However, the same signed midlets will NOT install on any Ericsson mobile or Siemens mobile we have tried. If we install them totally unsigned, they work (except for the usual security warnings etc..). So, we need help from someone that knows how to work with this, to get specific certs for Siemens, Motorola, Samsung etc to get a signed version of the app to work? Sign a midlet with several certs or? We need most of all advice and guidance from someone with experience from this specific field. The work can be done by us, but we need advisors!