1) You will need a "local loop" at each location. This is the leased line that connects your office to frame-relay providers point-of-presence (POP) at that location. The speed of these local loops will be based on the service (port speed, CIR) that you obtain from your frame-relay provider.
2) If you are not obtaining frame-relay service for all locations from the same provider, you will need to arrange for a "network-to-network" interface (connection) between the different providers involved.
>Or just subscribe from USA service provider will take care the whole setup ?
That would definitely make your life easier.
But here's the catch. Frame-Relay is a... fading technology. New installations have dropped significantly. And some frame-relay providers are not offering frame-relay to new customers. If you're an existing customer and you want to ADD new sites, they'll accommodate you. But if you are a new customer, you can not get a new connection.
The trend these days seems to be towards MPLS for private multi-access networking.