The second problem is an unrelated glitch in the current generation Android onboarding process, and while it’s possible to dig into it more, a faster solution would be to factory reset the Android device before installing the SIM from your iPhone, and complete the Android onboarding flow a second time, because there are too many carrier-specific edge cases to wrangle. It’s not related to the iMessage problem at all, but when you have both problems, this is what the symptoms look like.