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I have a Glomex WebBoat 4G Plus EVO unit on our boat. IT supposedly is compatible with both ATT and T-Mobile data SIM cards. It dual SIM card slots so you could use both. I recently bought a data SIM card from T-Mobile, but the Glomex unit doesn't seem to be recognizing the card. Using the WebBoat app, I can see that the unit is seeing mobile signal, but is dissconnected from the network, doesn't recognize that it is a T-Mobile nework, therefore, there is no internet connection via mobile. I have been on the phone with T-Mobile tech support and they are convinced that the issue is with the Glomex unit. I have tried calling the USA line for Glomex...no joy there. I am about ready to rip this thing off the radar arch and toss it!! Something that should be as simple as installing a SIM card is turning into a fiasco. Anybody have any experience with this?
It's entirely possible that the plan you have on that SIM won't use the celluar radio in the Glomex. T-mobile is sometimes 'picky' that way. Ask them what APN and PIN or password (if any) should be configured to use the T-Mobile data network. Have a T-Mobile tech confirm that the T-Mobile network sees the IMEI of the radio making a connection. This will likely require 'escalating' the support call to levels above the basic techs that answer the calls initially. You haven't mentioned if you've done that already.
With the literally thousands of different cell radio models out there, some carriers have limits on which ones they will or sometimes WILL NOT allow on the networks. And this sometimes varies depending on the data plan. If only to block use of a data plan from one kind of device from being put into another.
You might want it to be 'as simple as installing a SIM' but it often is not.