BARCELONA—The Samsung Galaxy S9 will be coming to all the major US carriers, and T-Mobile will be offering the least expensive units.

The Galaxy S9 will cost $720 at T-Mobile, $790.20 at AT&T, $792 at Sprint, and $799.99 at Verizon. The Galaxy S9+ will cost $840 at T-Mobile, $912 at Sprint, $915 at AT&T, and $929.99 at Verizon. They'll also go for $719.99 and $839.99 unlocked.

The phones will all be available on 24-month or 30-month payment plans, but we like to give you the full price you'll end up paying at the end.

The Galaxy S8 and S8+ launched for $720 to $750 and $840 to $850 respectively, so the S9 series is a little more expensive. Some of that can be explained by the S9+ adding dual cameras.

The S9+'s price is coming up pretty close to the Galaxy Note 8, which costs $949.99 at AT&T. But these two phones are now differentiating themselves in weird, not always visible ways: the Note 8 has an even bigger screen and a stylus, but has a slower processor and modem, and none of the S9+'s new camera capabilities.

Smaller carriers are also in the game. Xfinity Mobile will offer the phone with a $250 discount for porting a line over, and a $200 to $450 trade-in value for another phone; the company didn't give its final price for the phone, however. US Cellular will offer a $250 discount if you activate a new unlimited line, and up to $350 if you trade in another phone; it also didn't announce a price.

All the carriers will be offering promotions. Verizon has seven, of which the most important is a trade-in deal offering up to $350 off the purchase of a GS9. Definitely check to see if you can get more value selling your phone on Glyde, Swappa, or elsewhere, but here are Verizon's trade-in values:

• $350 credit – Apple: iPhone X, 8, 8 Plus; Samsung: GS8, GS8+, Note8
• $300 credit – Apple: iPhone 7, 7 Plus, 6s, 6s Plus; Google: Pixel, Pixel XL, Pixel 2, Pixel 2 XL; LG: G6, V30; Motorola: Z2 Force, Z Force; Samsung: GS7, GS7 Edge, GS7 Active
• $200 credit – Apple: iPhone 6, 6 Plus; HTC: 10; LG: G5, V20; Motorola: Z Droid, Z2 Play; Samsung: GS6, GS6 edge, GS6 edge+, GS6 Active, Note 5
• $100 credit – Apple: iPhone SE; HTC: M9, M9+; LG: G4, V10; Motorola: Z Play, Turbo 2; Samsung: GS5, Note 4, Note Edge

T-Mobile is offering up to $360 in trade-in value on phones listed here. We expect that AT&T and Sprint will also have trade-in deals, but we don't have the details on those yet.

Getting to Gigabit

Both AT&T and T-Mobile called out the S9's new networking abilities and frequency band support.

For T-Mobile, this is the third phone (after the LG V30 and Samsung Galaxy S8 Active) to support the carrier's new Band 71, 600MHz rural network. That network is available in 738 cities and towns right now, T-Mobile VP of radio network engineering Mark McDiarmid said, and it will expand dramatically at the end of 2018 as old TV stations move out of the frequency.

The GS9 will also get speeds around 20 percent faster than the GS8 on T-Mobile's network because of its support for 12 simultaneous data streams rather than 10, McDiarmid said. That trick requires the operator to have 20MHz-wide channels on a band where the phone has 4x4 MIMO antennas, and the GS9 fits the bill. This benefit will also apply to Verizon.

On Sprint, the Galaxy S9 will have 4x4 MIMO on bands 25 and 41, enabling it to hit potential gigabit speeds. This is a major step forward from the GS8, which wasn't a gigabit phone on Sprint because it lacked 4x4 on band 41. So we may see a significant speed improvement between the GS8 and GS9 on Sprint, in places where the carrier has 4x4 MIMO set up.

For AT&T, this will be the first Samsung phone with its FirstNet Band 14 built in. FirstNet is a special LTE network designed only for first responders and public safety officials, to keep their channels of communication clear while other networks are crowded with panicked civilians. While AT&T offers officials priority access to its other bands, Band 14 (which AT&T has only just started to build out) will be reserved just for government.