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AT&T tries to defend why it shouldn't let you unlock your phone sooner
(www.androidauthority.com)
This is a most excellent place for technology news and articles.
Personally I always always buy phones with two sim slots. It's super practical if you travel semi-often.
Idk about apple, but basically all of the mid-range androids have this feature. I guess this is about the US though, so it's probably Apple.