The T-Mobile Samsung Galaxy S5 will come in two storage options: 16GB, and 32GB. However, it appears that you will only be able to purchase the larger capacity variant online, as stores will sell only the 16GB flavor. The information comes from a leaked training document that describes the above-mentioned sales policy for Magenta.
While you can already pre-order your device now from the carrier, April (next month) is the month to look out for with regards to US availability. In terms of specs, we should expect the same internals, including the 5.1-inch Super AMOLED HD display, 2.5GHz quad-core processor, 16MP main shooter, and all the rest. For an in-depth look at the Samsung Galaxy S5, check out our coverage from the announcement event (and not only), as well as the video hands-on below.