I guess for the sake of posterity on this old thread, the following facts are true:
- Cricket was a small, regional CDMA provider that also acted as a Sprint MVNO and had a few other roaming agreements (this was the case when this thread was started).
- AT&T started their own prepaid GSM MVNO, Aio Wireless, in 2013 that ran on their network, but was sold completely separately and had taxes & fees included and a throttle.
- AT&T bought Leap Wireless (owners of Cricket) shortly after and in 2014 applied the Cricket brand to Aio (it got a redesign) and tweaked the plans slightly.
- Shortly after that (March 2015), the old CDMA network was phased out and those customers were either transitioned to Cricket's GSM network or left.
- This year, AT&T is moving all the Cricket customers off of third-party proxy servers (Jasper, XO, Zayo, etc.) and moving them in-house. With this migration, ping times have dropped to be in the same range as real AT&T service. The move also is paving the way for other modern technologies an features like VoLTE, Wi-Fi calling, and optional video throttling to save data usage.
Even though Cricket basically competes with prepaid brands like MetroPCS, Boost Mobile, and Virgin Mobile, AT&T has positioned it to compete against T-Mobile and Sprint, too (Aio was original conceived to fight T-Mobile on price without AT&T having to compete, among other things). iPhones tend to work great on the new Cricket and even AT&T-locked ones will work with no trouble (I bought a GoPhone 32GB SE from Best Buy for my dad), as Cricket appears to be using a former Cingular-era MNC that AT&T still supports on their devices.
There are certainly constraints (8Mbps throttle on LTE, very limited roaming, hotspot an optional purchase on some plans), but if you aren't picky, it's not a bad deal, especially if you have multiple lines on your account (groups are cheaper) and have good AT&T coverage.