Definition: Given a travel related situation, and given a specific question about the situation, summarize the question into a title
Input: I have an HTC A9s. I could not find it on the US page of the manufacturer so I went to the UK page.

According to the specs, it does have the US frequencies:

Network4

2G/2.5G - GSM/GPRS/EDGE:
850/900/1800/1900 MHz
3G UMTS (#UL):
850/900/1900/2100 MHz
4G LTE (#UHL):
FDD: Bands 1, 2, 3, 4, 5, 7, 8,12, 17, 28
TDD: Bands 38, 40
4G LTE (#UL):
FDD: Bands 1, 3, 7, 8, 20

Will I be able to use it in the US for calls and Internet?

Output:
Using a European (GSM) cell phone in the US