Can an Indian GSM phone be used in the USA? I'm considering buying the Oppo F9 Pro, which has a dual sim GSM slot. I currently have consumer cellular service with a nano GSM sim card. would I be able to import the Indian phone and use it here without any problems?
A quick search brings up this site:

https://www.frequencycheck.com/compatibility/XnDDU6Y/oppo-f9-dual-sim-td-lte-vn-ph-64gb-cph1823-f9-pro/united-states

Which indicates that the Oppo F9 Pro would only have 2/2.5G speeds on some US carriers with GSM and NO support on the rest of the carriers for signal or speed. It would appear to be limited pre-2008 data speeds in the United States and presumably still usable as a phone/SMS on supported carriers.