Well, guys, despite Google Voice setting being worded as "Receive text messages...also via messaging app" I just found out that the setting actually enables SMS forwarding that you get billed for. Worded properly, it should say that it is forwarding to your mobile number or also received through the carrier's SMS service. Because I do not use the service from the website where I can monitor the properly described setting and because the app's option was inappropriately described, I had no way to verify what it was doing. I could only trust that they would not make an option that says it is exactly the option I am looking for despite being inaccurate to say it that way and despite others in the industry setting expectations in line with what I was looking for (iMessage and BBM).
All I knew was that replies from the messaging app were coming from the mobile number (billed) and that GV did not warn that I could be billed for forwarded SMS. I expected that they would make sure users knew or else heads would roll. There was no way to see how it was received because it looked like it was working exactly as I was expecting and I found none of the other expected indicators otherwise (warnings, wordings, etc).
Tell everyone you had to get a new cell number and give them all your Google Voice number. Don't try and get them to use a separate number for texting as most people can't deal with that, just route everything from Google voice. Then call your carrier and tell them to disable texting on your line.
I've used this approach for more than a year without incident and know many other people who have done the same.
Sony is the one who screwed up everything else on your phone, they add and remove whatever they like in the process of adding their crapware to Android. Like I said the Xperia Play got universally bad reviews and you would have a completely different experience with any high end Motorola, Samsung, or HTC phone.
I've said this to those same idiots a thousand times and IT DOESN'T WORK. You can tell them to forget that your old number exists and they will still call/text your old number because it appears in the call history when you call them. My new boss has been texting me every couple days despite these SPECIFIC instructions. Granted, it will show your GV caller ID you jump through hoops and call through a Google Voice access/forwarding number, but that's really only easy with the native integration on Android and that's precisely the level of native integration I want GV SMS to have.
Now, Sony did not "remove" a notepad. Only Google is to blame for there not being a standard Android notepad app. You may expect Sony to include one and be disappointed that they did not, but I would rather had a standard one in the first place so this could not happen from any reasonable manufacturer. I set my expectations appropriately and blame the only one who can reasonably be expected to provide it if they care about Android: Google.