You're limited to the fx brokers you can use with NT. Right now that is IB, MBT and Gain.
They were going to hook up to the Hotspot servers too, and there was some good news AND bad news on that front.
The good news is that they got it to work with the Hotspotfxr platform, the bad news is that Hotspot sold their retail to FXCM.
- if you like to use a bucketshop, use Gain/Forex.com
- if you prefer ECN execution(like) but want as much leverage as possible, use MBT
- if you want a broker that makes you margin twice to place a gbp/jpy trade (or any of the other crosses if USD is you base) then use IB.
BTW, I use NT to trade fx and futures with IB.
(Sidenote: if you don't have the 10k to open an IB account, then stick with one of the other aforementioned brokers, like Oanda or MBT which allow you to trade in really small lots - $400 min on MBT and $1 min on Oanda)