Wireless JMS (WJMS) is indeed feasible over low bandwidth networks. For example, the iBus//Mobile Wireless JMS product works on 9.6kpbs GSM connections, and even on slower links. We did tests with bandwidth as low as 1000bps.
It is important to check that the WJMS product can run also without any TCP/IP stack. This allows you to run JMS with very low bandwith, directly atop a serial line protocol. Typically, JMS products do not provide this feature and are not optimized for low bandwidth.
The overhead of a WJMS message is typically 20 bytes or less per message, depending and the quality of service you expect (delivery guarantees, explicit acknowledgements, header properties, etc).
This was first published in February 2002