UPDATED: T-Mobile's 3G data plan capped at just 1GB

Go over the limit with your new G1, and T-Mobile may throttle your data speed to a mere 50kbps or less—pretty harsh, even by wireless carrier standards. Update: T-Mobile has wisely relented and removed the 1GB cap, at least for now (see below).

If your total data usage in any billing cycle is more than 1GB, your data throughput for the remainder of that cycle may be reduced to 50 kbps or less. Your data session, plan, or service may be suspended, terminated, or restricted for significant roaming or if you use your service in a way that interferes with our network or ability to provide quality service to other users.

The caveat comes just beneath a list of bullets describing what's possible with T-Mobile's $25-a-month 3G data service, including "viewing content-heavy Web sites," "viewing YouTube," and "downloading large files from an e-mail or a Web site to your G1."

Now, usage caps for wireless broadband data plans are nothing new—but usually, the cap is around 5GB, as is the case with AT&T, Sprint, and Verizon Wireless.

Of course, that data cap doesn't apply to your Wi-Fi usage—just whatever you download over T-Mobile's 3G network. And if you're just checking e-mail and browsing the occasional mobile Web site, you probably won't even come close to hitting the 1GB mark during a given month.

But if you are, in fact, "downloading large files" and watching YouTube all day—as T-Mobile's G1 marketing site breathlessly suggests—the 1GB limit could start to get pretty constricting.
 
The penalty for cracking the 1GB cap? You may get your data speed throttled to just 50kbps—slower than EDGE—for the rest of your billing cycle.

One question that remains to be answered is how aggressively T-Mobile chooses to enforce its 1GB cap. For example, Sprint reps have said that they'd only go after unrepentant bandwidth hogs, rather than users who've—once or twice—strayed over the 5GB limit.

Also worth noting: In the fine print, T-Mobile says that "some downloads, such as movies, music, and games, not included." Presumably, then, any songs you download from Amazon won't count toward the 1GB cap … right?

In any case, it's disappointing news. Let's hope T-Mobile gets with the program and raises the cap to 5GB a month, at least.

Update: It appears that T-Mobile has changed its mind about the 1GB cap, at least for the time being. Here's the statement I received at about 7 p.m. Wednesday:

Our goal, when the T-Mobile G1 becomes available in October, is to provide affordable, high-speed data service allowing customers to experience the full data capabilities of the device and our 3G network. At the same time, we have a responsibility to provide the best network experience for all of our customers so we reserve the right to temporarily reduce data throughput for a small fraction of our customers who have excessive or disproportionate usage that interferes with our network performance or our ability to provide quality service to all of our customers.

We removed the 1GB soft limit from our policy statement, and we are confident that T-Mobile G1 customers will enjoy the high speed of data access over our 3G network. The specific terms for our new data plans are still being reviewed and once they are final we will be certain to share this broadly with current customers and potential new customers.

So, the 1GB "soft" cap is gone for now; will there be a new, higher cap in the future? We'll have to wait and see, but I'm glad that T-Mobile is thinking twice about the 1GB limit.

Related:
T-Mobile soft capping 3G data at 1GB per month [Engadget Mobile]