While MetroPCS doesn't sell Samsung Galaxy Note phones as of March 2015, it was acquired by T-Mobile in 2013, so Samsung Galaxy Note phones designed to work with T-Mobile's network work with MetroPCS. However, only GSM phones work on MetroPCS service plans.
GSM is a popular standard; many phones branded as "world phones" use GSM technology. However, different GSM phones use different frequencies. Even though AT&T also uses GSM technology, it uses different frequencies for some of its data connections. Because of this, Samsung Galaxy Note phones used on a MetroPCS service plan might not offer 4G speeds. Basic calls, however, still work as long as the phone is designed for GSM networks.