I have the 50 min , unlimited tex for the United States how do I know when I've used the 50 min? Can I add more minutes to the plan?
It depends on the carrier you're with. With some carriers, you can directly check balance on your phone. Others you need to call customer service to inquire. There are some that have self service in their website. You simply have to register and log-in to your account to check your balance.
Let me know which carrier you're with so I can tell you your options.