I get to see dozens of third party jPOS gateway implementations just using 5% of jPOS capabilities.
People download jPOS just to use the ISO-8583 packing/unpacking and sometimes they don't even get to use the channels, multiplexers, servers, transaction manager. I see developers trying to stay away from Q2 probably because they don't know it, but it's quite simple to use.
So I wrote a little tutorial, http://jpos.org/doc/tutorials/jpos-gateway.pdf that walks you through the process of installing jPOS and writing a production grade gateway capable of processing thousands of transactions per second.
The tutorial has two parts, first you get it running (takes about 5 minutes), then the second part explains why that very simple configuration works.
The second part has plenty of links to the jPOS programmer's guide documentation (freely available), while it's just a couple pages, understanding it and following the links may take some more time and may raise some questions that we'll be happy to answer.