I have seen a fair amount of debate about how accurate the rumor is. Since I saw the rumor, I personally have wiped my phone 4 times to install a different ROM and never once lost 3G.
Also, I found the rumor somewhat amusing because it said the only Verizon phone that was "Safe" was the Motorola Devour which in my opinion is an utter piece of crap. EVERY person I know that has a Devour absolutely hates cuz the phones have numerous and repeated hardware failures. Thus I find it suspicious that it's the one "safe" phone. Sounds almost as though someones trying to dump all the Devours they can,,