Possible I'm missing it, put seems like if you are going to build a phone the first step would be to state what governements and networks would support it.

For example, appears that in the US that even if the phone would have worked with AT&T in the past, that as the end of 2016, that is no longer the case:

https://www.att.com/esupport/article.html#!/wireless/KM10848...