With Telstra's new offer of free access to Telstra Air hotspots across Australia until June 30 2016, I can only assume there would be customers from other carriers wanting the same thing, but don't want to pay for a recharge for a new service or switch over their current service to Telstra.
Well the good news is that you don't need to have an active recharge on you mobile service for it to be eligible for Telstra Air's Free Wi-FI offer.
So, you can buy a $2 SIM:
Activate it (the offer does not matter)
Put the SIM in a phone
Go to https://www.telstra.com.au/latest-offers/telstra-air-free-wi… on your phone
Press check eligibility and either sign up for a Telstra ID or activate with an existing one.
Remove the SIM from phone
You now have access to Telstra Air's Australian hotspots until June 30 2016, just login with your Telstra ID when connecting to any hotspots and your off. Enjoy!
Also if you are using this tutorial because you are a business customer that wants access to Telstra Air, I suggest using a different Telstra ID to the one with your business account on it, as some people have been reporting problems.
But if I want to receive an sms or make a call, I'd have to switch sims again.