There are multiple ways for you to purchase one of Samsung's current flagship devices if you're in the United States, you can pick one up on installments from a mobile carrier or get it on a conventional service contract. You can even buy it outright if you're not worried about spending that much money at once. Often eBay plays host to some really good deals that might interest you if you're looking to purchase the phone outright, and eBay has one right now for the Galaxy S6.
Carriers in the United States are selling the 32GB Galaxy S6 outright for north of $600 but you can head on over to eBay right now and pick one up for $499.99, which is the cheapest price yet for the unlocked variant of this smartphone. You'll get the G920i variant which is compatible with GSM and LTE networks, it has all the required bands to work on AT&T and T-Mobile. Another advantage of purchasing the handset through this deal is that you can get one in blue aside from gold, white and black. Carriers in the US don't offer the Galaxy S6 in blue. If you'd rather have the Galaxy S6 edge instead there's a pretty good deal on that as well.