Javaapplications will not download to other phones than Nokias via a NAMP 2.2 WapGateway. The same apps can be downloaded to the phones via Gateways of other operators, so it is not the phones or the applications.
Any idea what else it can be?
Some mobile phones (i.e. Siemens, Samsung etc.) using a direct HTTP connection from the dialinpoint to the JAR file.
You have to be sure that HTTP connection (i.e. Port 80) is allowed and the mobile phone will get an DNS server, which "knows" the host where the JAR file is stored.