I just got this email from Virgin Mobile (since it's not copyright protected I can post it here)
Starting February 15, 2011, if you go over 5GB in a month on the $40 Unlimited Plan:
Your data speeds will be limited for the remainder of the monthly plan cycle. During this time, you may experience slower page loads and file downloads and lags in streaming media.
Your data speeds will return to normal as soon as you buy a new Broadband2Go Plan.
This change will only affect plans bought on or after 2/15/2011.
I've had very good luck with Virgin Mobile's coverage map, so far they've been very honest about where it does and does not work. (AT&T who I had last year has a horrible map that tells big fat lies about coverage).
The speed varies widely. Some days I am zipping around at lightning speed, other days I am creeping along, but it's fast enough for my internet work which does require a lot of uploading. If you watch a lot of video streaming, then you may not be happy all the time. I avoid videos for the most part, but I do sometimes set my downloads to work in the middle of the night, that way it doesn't matter to me if they are fast or slow.
Skype phone works perfectly on it,(fast or slow) a huge plus since Skype is the cheapest phone around and free, if the other person has Skype too, so this is a huge bonus to talk to my friends for free.
AT&T calls me from their computer 4-6 times a day. I sent them a letter outlining the reasons for breaking my forced 2-year contract, still they ring my phone off the hook all hours of the day and evening. I guess they don't read their letters... Since it's a computer voice calling me, I don't get an opportunity to explain I wrote them a letter.
As far as I know, each company requires you to buy their specific modem/USB to use with their air-card. I don't think you can switch it around, as one poster wondered.
I am surprised that campgrounds are super slow to think about adding free WiFi to attract customers, or maybe it's just the campgrounds and parks I choose seem to never have it or it's a super pricey add-on. I know most of the pricey parks do offer WiFi, but even then, some of those limit your daily usage.