If someone is using Google Voice, do they need a data connection (cellular or WiFi) to be on in order to send/receive any SMS messages?
This seems to be a big limitation, as keeping data on all the time can really drain the device's battery (and can get expensive with all of Android's background data).
Also, signal strength for a functional data connection generally has to be stronger than the minimal signal required to send/receive traditional SMS messages. Inside buildings, it is commonly hard to get a data signal, but SMS messages can often still be transmitted/received.