So, wrap your brain around this one: both the Momentum and Elevate 4G mobile hotspot devices will go live on AT&T on August 21st, where you’ll be able to buy them — without 4G LTE coverage. A launch date for the service hasn’t been pinned yet, so you’d be using HSPA+. Data is priced as the following: 5 gigabytes of data for a monthly rate of $50 with any additional data consumed available for $10 per gigabyte, exactly like Verizon Wireless’ plan. If you’re okay with buying devices that support a network that isn’t out yet, then go right ahead on the 21st. Press release after the jump.