This may be of interest Phil (typing at the same time):
Troglodyte
Wow, well, what better way to spend a day.. here's some info that may save a few of those hours for someone as i couldn't find anything recent online, two visits to a Telstra shop and ending up standing ground at the business centre helped. A summary as this has cost a bit as well as time:
Telstra wont sell new Satphone other than on a plan ($30pm inc $10 calls), other companies and OS retailers will
As of late last year
prepaid Telstra mobile SIM
will work with an Irridium Sat phone, international roaming is automatically included on new services
Unfortunately not straight forward as its a bit of a gamble on how old the SIM is that the retailer tries to sell you.. Still a great option for emergency use and not much out of pocket if it doesnt work. Not much fun running out of credit in a (almost) emergency though...
Post paid (billed) is available (min $10 p/m) with no contract for those who own a compatible phone (from some source).
Unfortunately this isn't grab and go either, you'll need to now have been a (good) customer for 6mths prior. Int roaming can be enabled/disabled online but once int roaming is enabled
roaming bars will also need to be removed by telstra Emergency numbers never require account credit on mobile services
however, with no way to check and from what it's taken to get sorted I wouldn't like to rely on this however, something to keep in mind for anyone on prepaid mobile or sat services i suppose.
Those using older SIM with international roaming enabled may (
or not) have the roaming disabled
(without notice) in the future

and the rules may change with it disabled (and needing to be re-abled (ie by telstra or online)) under certain circumstances (noone all that sure what these were)
Really the only viable 2-way system available and clunky in use but there are cheaper usage options than at first glance.
Hope this helps someone, subject to change at whim but a good starting point.