About Google Voice on iPhone
Google Voice for iPhone allows you to use your iPhone to place calls and send text messages from your Google Voice phone number, and lets you take advantage of cheap rates for international calls. You can receive voicemail and text messages via push notifications, and the app is fully integrated with your iPhone contacts to make calling and messaging easier.
You can use the Inbox to listen to your voicemail messages or read transcripts, and add people you call often to your Quick Dial contacts.
When using Google Voice for iPhone, both domestic and international calls are placed through a US-based Google Voice access number, and will use the standard minutes from your cell phone plan. International calls are charged against your Google Voice credit, at Google Voice international rates. Text messages are sent through your data plan, so there are no text messaging charges for messages sent numbers in the US and Canda. Text messages received in Google Voice for iPhone are free; however, if you choose to have the text message notifications sent to your iPhone Messages app instead of to Google Voice for iPhone, you may be charged for received text messages (depending on your carrier).