I have had mobile broadband for 3 months. I got it simply because adsl was far too slow (3-5mbps on good days) and nbn was taking forever to be rolled out in my area with no ETA. TBH the speed of mobile broadband is not much better than my adsl, despite it being over 50mbps when it was first connected. I took it with me on holidays for over a week and consistently saw much faster speeds in an area I expected there to be no service at all.
Nbn is now connected and I was wondering if I cancel my month-to-month mobile broadband, does the SIM card get deactivated, and can I resume or sign up again to a month-to-month plan, say in 6 months (eg. when travelling again)?
If you are on month to month you can cancel whenever you like. Maybe use a prepaid sim in 6 months time as the postpaid card might be disabled. That's really no big deal as you can simply call into an Optus shop and get another postpaid sim on contract if you wish. Keep in mind that month to month deal may not be available second time around and 12 months may be the shortest period.