Carrier phones are all well and good if you need a subsidy or trade-in payment plan to make it financially feasible, but HTC has an unlocked phone with your name on it. If you can justify $649 to buy the phone outright, you can place your order right now.
The unlocked and developer edition One M9 should work on just about any GSM/LTE carrier, but HTC hasn't listed the specific bands for this device anywhere I can see. The only difference between the developer and unlocked devices should be the unlocked bootloader on the former.
You've got your choice of gunmetal gray or two-tone silver/gold phones right now. An all-gold unlocked phone exists, but is not available for purchase yet. HTC says the phones will ship in 3-8 business days if you order now. There is also 0% interest financing available with a credit check.