Carl,
the listener handler continually read from your queue and invoke your service passing the message read from the queue. I have found many bugs with this but 4 fixes using WM IS 601 and MQ adapter 3.0. Once installed all is ok.
If you do want to poll the queue and do a get each time, then I guess you could schedule your service to be called every n seconds.
hope this is of some help
Mike
#Integration-Server-and-ESB#webMethods#Adapters-and-E-Standards