Hi mate thanks for response.  
Just to clarify though, AnyConnect I presume is still going to require inbound 443 connections to the Meraki MX which from my understanding is an issue for this scenario as it is using a 4G Cellular only connection.  Is that correct? 
 
I'm not sure if there is something additional required to enable a specific APN(telstra.extranet) in the Meraki MX to enable it connect to this specific APN and then see these inbound connections. 
 
I think by default, on the ISP side(Telstra), they filter inbound connections on udp/500, udp/4500 or even tcp/443 for standard 4G services.
 
Philip earlier in this thread has mention Meraki May have to do something to enable a different APN on the MX...  "Once you have an APN you can use you'll need to open a support case and ask them to configure the MX68 to use that APN."
 
Cheers