As promised, AT&T has begun selling the Surface 3 LTE with 2GB of RAM and 64GB of storage. The 10.8-inch tablet with the additional 4G LTE hardware is available for $599 without a contract, $499 with a two-year contract, or $30 a month for 20 months under AT&T's installment plan.
Microsoft has also announced that its store website will have unlocked 64GB and 128GB versions of the Surface 3 LTE available starting today, with AT&T and T-Mobile SIM cards for the tablet also available at Microsoft Store retail locations. However, at the moment, the site does not yet show the tablet as being available. We will update this post when that happens. In addition, T-Mobile will begin offering the Surface 3 LTE to business customers in its @Work program starting July 31.
Update: Looks like Microsoft was a little too anxious as they have now updated their blog post:
"However, unlocked Surface 3 (4G LTE) will be available in the U.S. through Microsoft stores, authorized resellers and partner retailers in late August."
Looks like you'll have to wait a bit longer if you want the unlocked version.