ATT GoPhone?

Hello guys, I am thinking about getting an AT&T gophone and then using unlocked samsung galaxy nexus with it. What are the advantages and disadvantages in using a prepaid phone? I am planning to go with the $50/month unlimited plan.

With samsung nexus's price($350) and 24 months of att's services( $50*24 ), I will be spending $1550, which appears to be more cost effective and I can use unlimited instead of 300MB when I go with the basic data plan in the contract.

Thank you for your thoughts :)