netw0rk
If the phone doesn't "render" the message, you might be safe from specific attacks against vulnerable parser components. MMS had a vulnerability way back in the media processor.
But there are several vulnerabilities in the class of zero click SMS which are vulnerable without rendering. Basically as the message reaches the phone baseband. If it's a user app that intercepts the message and just doesn't display a notification, rather it sends to the mobile router, then you're probably still vulnerable to the majority of attacks.
But it looks like this model allows you to put the SIM in the router instead. If you do that, you might avoid your phones vulnerabilities and exchange them for the mobile router's vulnerabilities.