Be very very careful if you do that.

The data plans on some embedded modems are quite different from consumer plans. They are specifically designed for customers who have a large number of devices but only need a small amount of bandwidth on each device.

These plans might have a very low fixed monthly cost but only include a small data allowance, say 100 KB/month. That's plenty for something like a blood pressure monitor that uploads your results to your doctor or insurance company.

If you are lucky that's a hard cap and the data plan cuts off for the rest of the month when you hit it.

If you are unlucky that plan includes additional data that is very expensive. I've heard numbers like $10 for each additional 100 KB.

I definitely recall reading news articles about people who have repurposed a SIM from some device and using it for their internet access, figuring that company would not notice, and using it to watch movies and download large files.

Then the company gets their bill from their wireless service provider, and it turns out that on the long list of line items showing the cost for each modem, a single say $35 000 item really stands out when all the others are $1.

If you are lucky the company merely asks you to pay that, and if you refuse they take you to civil court where you will lose. (That's what happened in the articles I remember reading, which is how they came to the public's attention).

If you unlucky what you did also falls under your jurisdiction's "theft of services" criminal law. Worse, the amount is likely above the maximum for misdemeanor theft of services so it would be felony theft of services.

Example: https://news.ycombinator.com/item?id=2509967 (the original source is gone and not in the Wayback Machine)

Through what technical or legal mechanism is the company identifying or locating you - assuming you never logged in or associated the product with your identity?