I didn't see a thread here for this MVNO, so I thought I'd start one.
Sign Up
Their free BYOD activation promo has expired, but they still have a $0.99 one:
http://www.freedompop.com/byodpromo8
Starts you on two free trials, so be sure to downgrade under both Plans AND Services in the first month.
Free Data
Basically, you get 500 MB free data every month, plus another 500 MB bonus every month for connecting with 10 "FreedomPop Friends" in your account. That bonus persists as long as you keep at least 10 "Friend" connections (meaning, you don't have to add 10 new ones every month). Add as many friends as you can from the most recent pages of this thread at Slickdeals and you should be good for 1000 MB free data per month going forward:
https://slickdeals.net/f/5276432-freedompop-friends
You also get "minutes" and "texts" on the free plan, but only through FreedomPop's VOIP app. I don't even bother with that, I just use Hangouts / Google Voice as my VOIP provider of choice. You need to install the FreedomPop Messaging app to activate the device, but once you are activated, you can uninstall it and continue using the free data.
Add-on for "real cell" minutes
The "Premium Voice" add-on ($3.99/month) gives you 200 real cellular minutes per month. It used to be outgoing only, and there was some trickery involved to force it to use cellular, but they've since added a "Incoming Premium Voice Preference" which you can enable in your account settings. I just tested and it worked for incoming and outgoing on the native phone dialer. Of course, it uses your FP phone number, but you could use it in conjunction with Google Voice and forwarding to use your GV number on it. (Real cell minutes on Sprint aren't that valuable to me, so I don't plan to keep this "Premium Voice" service beyond the free trial.)
GSM SIM cards
This is all for their BYOD CDMA service. They also offer SIM cards for GSM data service on the AT&T network, although "Premium Voice" isn't an option there and the free data allotment is slightly lower -- 200 MB base, 700 MB total after adding 10 "FreedomPop Friends." The LTE SIMs are currently $1.99 (and during the checkout process you get offered a second $0.01 "bonus" SIM) -- you can buy a bunch and rotate through them on the same device, if you need more data. They also have "Global" GSM SIMs (for $0.01) that work internationally as well as in the U.S. but they aren't LTE -- maybe a good choice for a backup / international travel SIM.
Overages / Billing
If you don't have a balance on your account, they will bill you when you are within 100 MB of your monthly plan limit. So if you have 1000 MB free per month, they will charge you $15 after you hit 900 MB. That $15 goes into your balance and will be used to pay overages if you exceed your plan limit. Their stated reason for charging before your limit is because of reporting delays. You can add $5 to your balance to cover overages instead (called "Disable Auto-Topup" in your account's billing settings) and your balance won't expire except you will need to click to renew it after awhile, I think. (Likewise accounts/plans don't expire due to inactivity, but they can go dormant if unused for awhile and you'll have to sign in to "re-activate" (for free) to get back online again.)
You can keep a credit card on file, or connect it to a PayPal account. I formerly used a prepaid card on my account but they have blocked that now. Many folks use a virtual credit card from their credit card company; others set up a special PayPal account with minimal funding. Still others link FreedomPop to PayPal, but then revoke the authorization in PayPal. I guess if FP tries to bill you though and it fails, they could shut down your account.
I'm pretty careful, and I don't use a ton of data anyway, so I keep a zero balance and haven't had any problems. I set my devices to limit mobile data at 200 MB below my plan limit (although I've never reached that threshold). I also use this FreedomPop API Python script as a basis for automating my usage checks / reports:
https://github.com/dodysw/fpopclient
My Conclusion
I happen to have both the CDMA and GSM models of the LG G2, so I have them both on FreedomPop free data now, sharing one Hangouts / Google Voice number. I will switch between the devices as coverage and data usage dictate.