T-Mobile and Sprint are both making a big splash today with the introduction of some too-good-to-be-true data plans. Both companies' new plans offer unlimited talk, text, and — importantly — data, but both companies' unlimited data come with big asterisks beside them.

That's because their data plans have some significant limitations. T-Mobile's plan, called T-Mobile One, limits all video playback to low-res 480p. Sprint's plan, called Unlimited Freedom, has the same video limitation and then goes even further, limiting music streams to 500kbps (which is relatively high) and gaming to an extremely slow 2Mbps. T-Mobile will let you avoid that limitation if you pay an extra $25 per month per line; Sprint doesn't seem to offer an option.

Video and tethering are far from unlimited

There are also limitations around tethering. T-Mobile offers tethering but only at 2G speeds. That might be helpful in a pinch, but it's generally unusable. To get LTE tethering, T-Mobile customers will have to pay $15 extra per month for every 5GB of data. Sprint is a bit better here. It offers 5GB of LTE tethering and then bumps you to 2G after that.

Sprint's Unlimited Freedom Plan will be available starting tomorrow. It'll cost $60 per month for the first line, $40 for the second, and $30 for additional lines. T-Mobile's One plan doesn't launch until September 6th; at that point, T-Mobile will start phasing out its existing Simple Choice plans. Some may stick around, but it sounds like T-Mobile's current thinking is to move toward the One plan exclusively for post-paid. T-Mobile's One plan is also fairly expensive, at $70 for the first line, $50 for the second, and $20 per line for the next six lines.

Update August 18th, 3:13PM ET: Sprint says its unlimited plan includes 5GB of data for tethering; the story has been updated to reflect this.