FreedomPop's elusive Global SIMs are finally available again. The first and only time they were offered before they sold out in a couple of hours. Follow the source link below to order before they sell out.
The tri-cut SIMs work in unlocked GSM phones and offer 200 MB of data per month in 25 countries, including the US. You can earn up to 500 MB/month in additional data by connecting with FreedomPop friends. See this SlickDeals Forum thread where FreedomPop users share their email addresses so that other users can add them as Freedom Friends. It only takes a few minutes to gather up a dozen or two email addresses and enter the on the Freedom Friends page on the FreedomPop site for a quick 500 MB/month boost.
I have one of these SIMs and it works well. The SIM has a 3 UK Mobile Network Code which is why it requires an unlocked phone. It will register on either AT&T or T-Mobile in the US although it seems to prefer AT&T. Data is HSPA+, not LTE but it's perfectly adequate for most uses. Data seems to be routed through the UK which is likely responsible for the high 300 ms pings I've seen. Voice calling using Hangouts or FreedomPop's own app tends to have a lot of latency and occasional dropped words probably because of the high pings. Given that the service is free I'm not complaining.
Possibly because of issues with voice calls, FreedomPop is not including voice and messaging services with this batch of data SIMs. FreedomPop is recommending using Hangouts, WhatsApp or Viber for messaging with no mention of calling at all.