Improve connection over what? What are you connecting to currently that is giving you issues?
Tough to say without that info, but a hotspot would probably help... If you're having range issues then the hotspot being in your vehicle will take care of that, most likely.
Like Jokiin mentioned, hotspots can be finicky when it comes to going to sleep.
Though I do believe someone else mentioned the Nighthawk worked for them, might wanna do a quick search on that and reach out to them to see what their experience is.
Keep in mind, connection issues on BlackVue seem to be known and currently being worked on from the sounds of it.
You might want to push through and wait for the firmware update before you invest in something else.
Unless you know it'll be a better solution either way.
What kind of phone is your son using?
iPhone as well?
Is his phone connecting to the dashcams wi-fi?
Or is the dashcam connecting to the phone's hotspot?
It makes sense that if the phone is connecting to the cameras wi-fi (for app use/settings/viewing the feed/etc.) he wouldn't have any internet.
Since the phone thinks it's getting internet from a camera that doesn't give off that kind of connection.
He should still get calls either way though. If he's using an iPhone, an SMS that is sent to other iPhones - is called iMessage and ISN'T an SMS, it uses data to send (so if the messages are all blue, you know it's an iMessage.)
If the messages are green, then it's a text message/SMS which should work fine, just like the phone calls.
Android is more of the same, but it usually uses regular SMS over some built-in messaging platform.
Though a lot of people use various different messaging apps that use data to send and receive.
I have not tried this personally yet, but there is a setting on the phone that if your wi-fi isn't great your phone will auto switch between wi-fi and cellular.
On iPhones it's called Wi-Fi assist, which is located in Settings > Cellular > Wi-Fi Assist
Android manufacturers name this feature whatever they choose, so harder to tell you what it's called without the brand of the phone.
Another fix is to just turn off the wi-fi on the dashcam, probably not actually using it most of the time anyway.
Though you might not want to tell your son this info since it's probably better that he doesn't get notifications as much when driving!