SIM cards
SIM cards can be purchased in any shopping malls. The closest mall is SMITH HAVEN [1] which is connected by bus. In this mall, you have outlets for Verizon, TMobile and AT&T which are the major service providers in the US. All of these networks have good connectivity in the state of NY. When you go to buy a SIM, they usually ask for an ID (international ID is accepted), a deposit (around 50$), cost of a new SIM card (~25$) and SSN number if you need to buy a phone on contract with the network.
Most networks in the US come with unlimited text and call to anywhere in the US, Mexico & Canada. The data plan is what decide the monthly cost, you can opt for 1GB as we are usually connected everywhere by WiFI. Also, when you have a 1GB plan and it gets exhausted, you still have internet connection but at a lower speed (2G data).
An individual data plan costs around 40-45$. It is cheaper to club with other students or family members in the US.