Sending text messages using Google Voice can be setup to avoid text messaging charges on your bill. This is because the text messages go out via data link to Google Voice. This explains why you cannot send text messages using Google Voice when no data connection is available. However, you can send text messages through the Google Voice Application when you are on your provider's EDGE, 3G, or WiFi networks.
Some have a Google Voice Number, and they associate multiple phones with their Google Voice Account. They do this on Android phones with the Google Voice application installed and other phones that may not have the Google Voice application installed on them. This means that, for the phones that have not installed the Google Voice App, text message charges will appear on their bill even if they are subscribed to Google voice. This is because the text messages are no longer being transmitted through their data network, instead they are transmitted directly through the carrier's SMS channel. The carriers charge a premium for that service.
Receiving text messages, even through their Google Voice Number will show up as an incoming text message because Google Voice will send you incoming text messages through your carrier's SMS channel. The good news is that you can set things up to avoid the charges!
Follow these simple instructions:
Access your Google Voice Account online. Go to the account settings and leave the "Forward phone to your cell phone" checked. Then, go into the "Voice Mail & SMS Tab" to uncheck "Send SMS to This Number"
Now, on the same menu, check the "SMS Forward" and enter your e-mail address there. (Use the e-mail account that you set up on your Android phone.)
After making these changes, any text message sent to your Google Voice Number will be posted as an e-mail message. Read the "email" and your reply to that "email" will be forwarded out to the original sender as an SMS by Google Voice. Therefore, no charge will appear on your account for either receiving or sending text messages.
The Google Voice Application is a great tool. Use it wisely, save money, and enjoy its benefits.