Finally the keyword popped into my head. Keyword is "Benefon", a manufacturer that goes the extra mile with things like dual-sim phones, and phones with GPS built in (gps built in
6-8 years ago).
Something called the "Benefon Twin" does dual sim.
See:
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Note, by reading between the lines get the impression that it's still only one sim at a time in actual operation. There's a bunch of technical issues that make having both sims working and subscribed at once substantially more complex. I'm not going to go into them here though, they should be pretty obvious.
Hope this helps,
GB