Can I buy a SIM card in the States and use it in my phone?

Well you have to check your phone if its a TRI BAND , If its a dual band you cannot use it to different countries aside from our country

Well if you are in roaming then it is very much possible that you could use it. You may also contact your carrier and ask about if it is supported or the network is one of their partners. But just a reminder that it is very much expensive especially when you will use it for data (just like browsing and almost for anything).

I suggest that don't buy a sim in usa if you are going here in philippines. You cannot use that sim because the network in usa is not available here. When you arrive here in Philippines buy a sim here. You can use Sim in the Philippines to communicate with your friends in the USA.