If the developer possesses the original source code (typically Java for J2ME or C/C++), the process is one of migration :
Converting JAR (Java) files to VXP (MediaTek MRE) format is not a simple file-extension swap because they use entirely different runtimes. To run an application on your feature phone, you must either find a native VXP version or use specialized conversion software. Online Conversion Tools jar to vxp converter online
If you must use an online jar to vxp converter , treat it as a quick experiment for small, simple JARs (dictionaries, e-book readers, basic puzzle games). For anything else—especially games—use the desktop tools or an emulator. If the developer possesses the original source code
(Invoking RelatedSearchTerms for helpful follow-ups.) simple JARs (dictionaries