After signing in to your google account from the gvoice app, google adds your phone's number and verifies it by sending a text; the message is the following: "

After signing in to your google account from the gvoice app, google adds your phone's number and verifies it by sending a text; the message is the following: "Google Voice will now verify your phone number by sending a text message from your phone to the Google Voice service. You will be charged your carrier's standard rate for text messages." This happens the first time you log into the app, but it wouldn't surprise me that something similar happens from time to time to verify your phone number, a warning would be nice though.