> The main problem with using phones is the cost of the SIM plan. Over
> here, $15 AU per month (per unit) is probably the cheapest, and too
> expensive IMO.

Could you not use a pay as you go SIM in the phone at the point that needs 
to send an SMS?

On the other hand, if you have multiple units connected by Wifi, maybe you 
could have one unit that sent an SMS for all of them, as needed. 

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