All I know is I am not worried about any 5gb data limit on my everything family plan. This same spat of 5gb caps went round and round a year ago and even with all the fuzzy wording out there, in the end, it only applied to the data card plans and had nothing to do with the phones.
I also cannot find FCC statements regarding anything to do with 3g data. To me that is a another carrier cop-out similar to the "bandwidth shortage" created by the HSI providers to justify caps and extra fees.
Don, I think the verbiage is confusing. Mobile Broadband in the past only referred to the data cards, not the phones. Now carriers could have changed it, but this certainly would be a TOS change and if they started applying this to the phones, we would have all gotten notices and the forums would be abuzz about it, which they are not. I would even bet you'd see stuff on engadget and other sites.
Btw, if you search sprints online customer service forums (which are monitored by sprint reps and they actively post on them), the 5gb caps are only referenced with data cards, not a single thing about data capable phones.
Edit:
Just got done with online chat with sprint rep, they confirmed what I have in an email from earlier this month
You: Can you clarify the 5gb data cap
Kate: The 5GB cap only applies to data cards or PAM plans, not data capable phones.
You: What about tethering?
Kate: Tethering would be a PAM option unless you used 3rd party software to enable tethering, in which case it would be at Sprint's discretion if you violated your TOS of your phones data plan. Also please noted, no caps exist on the 4G network, just 3G.
You: Thanks, just wanted to check.
Kate: Thank you for choosing Sprint.
Now I use my phone alot, but honestly I have only reached 5gb + a few times in the years I've had a smartphone with sprint. But I'm sure if sprint saw my usage all of a sudden jump it would cause a flag in their system. For me, it's pretty hard to hit 5gb of phone data, whereas using a datacard or tethering, it's would be relatively easy to hit the cap with just normal use and loading non-mobile optimized websites and downloading (I don't do much downloading of items to my phone and what I do download is very small phone related stuff)