You'll need to already have an AT&T roaming option on your plan, though
Boingo today announced a deal that will give the former access to the latter's Wifi hotspots at locations worldwide for no additional charge. AT&T customers already have access to Boingo hotspots in major international airports; this expands the coverage even further.
There is a slight catch, however, as you'll need to go through AT&T's Wi-Fi International app to get access, and that requires you to have one of AT&T's international roaming plans. The 300MB plan runs $60 a month, or you can get 800MB for $120 a month. Then you'll get up to 1GB of Boingo Wifi data on top of that.
Reciprocally, Boingo customers traveling in the U.S. will be able to use AT&T's Wifi hotspots while they're here.
Source: Boingo PR