Alternatives to burner phones?

I found that swiching sims is easy enough, but I'm not a fan of buying new phones as often as I do, partially for monetary and partially for ecological reasons.

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What are my options here? One idea I had was to use a sim with modem-manager-gui (on linux), and a GSM modem, but I don't know of any privacy respecting modems that can switch the IMEI (since switching the sim - the IMSI is not enough)

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Another alternative …

burner phones privacy