Will be iPhone work in the USA?

I have an iPhone 6 and I'm with the network called 'three' , I'm living in Ireland, and I'm travelling to Boston USA in July, can I use my iPhone for data and calling in the US? Will it cost extra?

As for the cost, it depends on your cell phone company. Ask them. Usually it costs a lot extra - at least for US folks going abroad.

The phone should work in the US, but again, call the cell phone company.

Advice, keep it on Wi-Fi because data is what kills you. Turn off the data.

And use regular messaging not imessaging - which uses data.