T-Mobile’s new unlimited data plans have yet to launch, but the carrier is already making some changes to them.

Earlier this month the operator introduced “T-Mobile One,” a streamlined plan that offers unlimited voice, text and data for $70 a month for a single line, $50 for a second line and $20 for additional lines (up to a total of eight). But the new plans drew flak for limiting video streaming for 480p and capping hotspot speeds at 2G.

This morning the carrier said mobile hotspot service for T-Mobile One customers will be on its 3G network, however, increasing speeds from 128 Kbps to 512 Kbps. And it introduced one-day HD passes, enabling users to access unlimited HD video streaming for 24 hours for an additional $3.

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Lastly, T-Mobile introduced a premium unlimited plan for heavy data users. T-Mobile One Plus, as the latest offering is branded, includes unlimited HD video, unlimited 4G hotspot access and 3G data roaming in more than 140 countries and destinations for an additional $25 per line.

The operator said both new plans will be available Sept. 1, five days earlier than T-Mobile One had been scheduled to launch.

Neither plan is absolutely unlimited, however, as T-Mobile will continue to throttle high-end users once they’ve reached a specific monthly threshold. “Like with every plan, customers who use more data than 97% of our customers (currently over 26 GB per month) will have their usage prioritized below other traffic and may notice slower speeds during times and places of congestion,” T-Mobile said in its announcement.

Sprint announced its own unlimited data plan two weeks ago as well, offering a single line for $60 a month and a second line for $40 more. Analysts generally agree that both unlimited offerings are likely to entice some wireless users to switch from Verizon and AT&T, neither of which offer unlimited data packages to all consumers. But some analysts have also expressed concerns about how well the networks of T-Mobile and Sprint will handle the increased traffic the new unlimited plans are likely to drive.

For more:

- see this T-Mobile press release

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