Hello Takeasecond. I am on unlimited grandfathered plan as well, and I was told that there are 6 cards (3G Only, you cannot use a 3G/4G card, or a 4G only card) that we can upgrade to without jeapordizing our contract:
USB
- Novatel Ovation (he didn't say which model exactly, but since it has to be a 3G only one, maybe the U727?)
- Sierra Wireless 597 (his personal recommendation, I bought one but never plugged it up)
- Sierra Aircard 595U
PCMCIA
- Pantech PX-500 (the "ol' reliable", but lately it seems that this might not be so reliable after all, see »
PX-500 users... Time to upgrade. for more information)
- Merlin C777
- Merlin S720 (what we upgraded to after our second PX-500 started giving us issues, this has been working great for us, as long as we don't let the card overheat. We now shut it down for about 4 hours every day, whereas we used to leave the old PX-500s running for weeks on end without any issues)
- Merlin S620 (does not support EVDO Rev A, so you probably don't want to bother with this one)
I was told by a friend that the USB modems are a little "dicier" than the PCMCIA ones, so I've been trying to stick with using those.
You must do an ESN swap through the Sprint Online Chat option. I went to the Sprint Connection Manager "activation" pages and walked through those with the online chat agent. Be very very clear that you do not want to change your plan at all. I just did one a few weeks ago to move to the Merlin S720 and it's been working fine. I am not using Sprint SmartView, I am using the old "Sprint Connection Manager" software instead. I've had problems with SmartView in the past.
However, it is interesting that you should mention the issues you were having on 1/17/2014, because we were seeing some crazy weird stuff that night as well. Hardly any sites would work except for Google and anything under Google's umbrella (like Googlecache). I messed with the settings a bunch trying to tweak and see what was wrong, but eventually I gave up and turned the computer and modem off. Thankfully the next morning it was working fine, and has been working fine since (it's what I'm using right now to make this post).