MIDlet can communicate with native applications using standard protocols (HTTP, sockets) on the same host using the local loopback address. This gives possibility to offer services that are not available in standard Java APIs.
There is an extensive how-to example in Symbian Developer Network named Extending the Reach of MIDlets: how MIDlets can access native services.
One use case for this mechanism would be autolauching MIDlet in a boot. MIDlet could register UDP push connection, which would be then triggered by a native application during device startup.