T-Mobile is offering some customers “free” data use when travelling abroad. The catch is that you’ll have to pay extra to get a decent speed.

The deal starts automatically on October 31 for anyone on a “Simple Choice” plan, which already offers unlimited texting, voice calls and data use in the US. It only applies if your plan already has domestic roaming capabilities.

When the deal takes effect, customers will get unlimited data and texting in more than 100 countries. Voice calls (whether to local numbers or back to US numbers) will cost 20 cents a minute on top of the usual monthly subscription.

The main catch is that the free data is only delivered at up to 128 kbps, or just twice that of old-school dial-up. In other words, it’ll do for e-mails and limited web browsing, but that’s about it.

T-Mobile says if you want faster speeds overseas you can buy one of three plans: one day with a 100MB limit for $15, seven days with a 200MB limit for $25, and 14 days with a 500 MB limit for $50. Those will run at faster speeds, though the precise details aren’t clear; this may be because it varies with local networks.

The small print also reveals that you can only use the free data overseas for six weeks at a time. During any three month period, at least half your data use must be in the US.

Another, more minor, catch comes if you use Wi-Fi overseas and make a VOIP call such as through a Skype app. There’s no charge to receive calls or to call back to the US. However, calls from abroad to a non-US country will have a flat charge of 20 cents.

T-Mobile is banking on the idea that the price cuts won’t necessarily win customers away from the bigger networks, but rather will capture customers who’d not previously bothered with overseas use. The company concedes that most people who are willing to pay high fees for fast access overseas are probably actually getting the bill paid by their employers, who prefer to use the major networks.

It’s intriguing to see a network use a heavy reduction or abolition of international roaming charges as a competitive tactic. In the absence of similar moves in Europe, regulators from the European Union have proposed a total ban on roaming charges between EU member countries by 2016.