Right, but the "problem" is that unless you're using SMS forwarding (and any carrier fees that incurs), then an incoming SMS to your Google Voice number isn't a

Right, but the "problem" is that unless you're using SMS forwarding (and any carrier fees that incurs), then an incoming SMS to your Google Voice number isn't arriving to your phone as an SMS message. Instead, the Google Voice app is polling the GV service, not unlike checking email, and notifying you of any new messages it finds. How instantaneous you get the message depends on how rapidly the app polls. The official Google Voice app on Android waits a few minutes between polls. The 3rd party "GV" app lets you set it more aggressively (though naturally, there's a battery trade-off that comes with doing so).