Beg to differ all you want, it doesn't change the fact that Google Voice app does not use SMS/MMS protocol.
Do any of the 3rd party SMS/MMS widgets let you see your Google Voice texts? If any of them do (and I still haven't found one) then it has seperate code to enable it to specifically poll Google Voice instead of just the SMS/MMS apps.
In the end, you may use Google Voice for free texting all you want, but it doesn't change the fact that Google Voice app is not a SMS/MMS app; it only allows you to send SMS/MMS through Google's proprietary servers.
I understand what you are saying and actually agree with your assessment. However, if it acts like an SMS client, looks like an SMS client, and smells like an SMS client, I'd consider it my SMS client. Now can we have it be recognized by MIUI as one so I can have a choice of which one to pick on my LOCK SCREEN? Please.
The funny thing is that this choice is there in MIUI when you go to contact, click the picture of a contact, and choose text from the opened up menu. It gives me a choice of native client, handcent, or google voice with the option box to be used by default at the bottom. So if can be there, don't you think it not being at the lock screen is just an oversight? Cheers.