While it is true that we have to be careful when comparing reception levels of different phones, and 3G vs. 4G, remember that 3G is still always used for voice, even if you are in a 4G LTE area. LTE is currently only used for data by Verizon, it might change in the future with voLTE. Since 3G uses 800 and 1900 Mhz, and 4G uses 700 Mhz, they will behave completely differently (building penetration, etc...). Now given all this, 3G is CDMA and uses the MEID to activate, whereas 4G is GSM and uses the SIM card to activate and talk to the network. We really have two phones in one in order to transition to LTE and keep the compatibility with 3G until LTE can replace 3G for voice and data.
It seems to be very important to follow the activation process in order to activate both 3G and 4G. Some people jump too fast and seem to only end up with one or the other. Follow the "getting started" guide for activation.
The Verizon variant of the phone has to deal with this challenge on the data side: use GSM when available, if not switch completely to CDMA. I have a feeling that this is the reason why the WiFi toggle is not available on this SGS3 vs. all the other GSM carriers. On those phones, when you turn on WiFi the phone switches from GSM to WiFi for data. On Vz it is more complicated due to the fact that the phone uses CDMA and GSM for data, but needs to keep CDMA ON for voice all the time. So the standard Samsung WiFi toggle can't be used, otherwise it would probably turn off voice CDMA service if you are in a 3G only area. Makes sense?
Coming back to the thread subject of signal strength, I still think that it is a valid point to compare 3G phones with the SGS3, simply because that is the network that everyone uses for voice. Some will argue that they primarily use their phone for data, but most people want their phone to have great voice capabilities when they need to talk. For me, this is the #1 reason to choose Verizon over the other providers, I need voice coverage 100% of the time even though I might not use a lot of minutes. I just need the 3G to work. This is why I pay extra for the best network in the USA. If I can get 4G data speeds in more places than other providers then that's fantastic, and eventually get voice over 4G. But for now I am buying the renowned 3G nationwide coverage that no one else can provide.
In summary, 3G on the SGS3 should be compared with existing 3G devices in order to evaluate the quality of the voice service.
Obviously I did not receive my SGS3 yet, can the lucky owners tell us if it is possible to force 3G only, and if the dbm reading changes at all when you do that?