Regardless if the main "code" is the same, there are absolutely account changes that must take place when you switch from a 3G phone to a 4G phone. If you have a 4G phone now you can look at your account and see it riddled with 4G "codes" (4G DATA TRANSPORT, 4G INTERNET ACCESS, 4G APPLICATION ACCESS, 4G No Roam - USA Only, Mobile Broadband Connect and Mobile Hotspot for 4G LTE Smartphones, <- my fav)
I have worked in wireless for a long time and I have a sneaking suspicion that anyone hanging on to a 3g phone will be awfully sorry when the plans roll out this summer. I have seen first hand that the best way to keep what you have is to not make any plan changes period.
You can't deny that there are changes that are performed to the account. I hope that Verizon does do the right thing and allow these changes to be made once the system is updated with new plans. I have personally worked for Sprint & AT&T and have dealt with MANY grandfathered "codes" in my lifetime and I know that a lot goes into building an account profile. I hope your confident statements are based on more than just your interpretation of Verizon's "clarification statement" because it's not like there aren't multiple ways they could go from there....
A few VZW phones have radios that support the SVDO capability. It's not just those two HTC phones, the LG Spectrum can do this also. Verizon is very, very quiet about this feature, probably because it isn't available product-wide.
I did not realize that it was up to the phone chipset, thought it was mostly up to the network technology itself. Thanks.