Besides a good Java IDE with mobility support, you need to download and install special SDKs from the phone manufacturers that you wish to support. The main thing you want to get your hands on is of course the phone model emulators and the special java libraries that they might use, but the SDKs also often include software to be able to deploy your midlets to the phone. The Nokia Series 40 phones, for example, only supports deploying midlets to the phone via their own deployment software.

Even if you don’t have a particular phone you want to support, it’s good to have a couple of different phone emulators to try your midlets on. Believe me, you can’t trust the standard emulators in the Wireless toolkit, you need emulators that are updated by the same people that make the software in the actual phones.

If you want a starting point I recommend that you try out the SonyEricsson J2ME SDK. It’s easy to install, it runs well together with Netbeans and the SE emulators launch pretty fast (compared to many other emulators, that is). You can say much about the quality of different phone brands, but the J2ME JVM in Sony Ericsson’s phones is the fastest and the most stable one I’ve encountered (and I’ve tested a lot of them), so if you need a good phone use when developing games for, you should get a Sony Ericsson. And no, they don’t pay me to write this :)