I was looking for the answer to this as well. When I stumbled across it, I created a user account here just so I could share it with you folks.
Here's the answer and the fix.....
I had the same issue. Google Voice installation. Rooted EVO running CM7. Kept getting the "Press 1 to accept this call" and SMS going through Google Voice. I uninstalled Google Voice...that did not fix it.
I reset/wiped my phone and flashed CM7 to it again. Even THAT did NOT fix it..
The fix....
The fix is not on your phone, it is linked to your Google account. Remember, Google is a CLOUD Service provider and everything linked to your Google account is in their cloud services. So you first must login to your Google account online. I found it easier to go through my market account to get to where I needed to be to fix this annoying issue.
Go to market.android.com and login to the market.
Once there, click on your name in the upper right corner of the screen and select "Account Settings".
Then on the next page on the right hand side of the page select "Products". That takes you to the "Your Products" page. On that page find Google Voice (probably labeled simply as "Voice"). Even if you have removed Google Voice from your phone, the settings remain on your account, that's why the conditions persist even if you uninstall!
Click on "Voice". There you will see the history of all the texts and voicemails that have annoyingly been sent there.
In the upper right corner, there is a SETTINGS Icon (look like a little gear). Click that Settings Icon, and viola, you are in the cloud settings for Google Voice.
Across the top of the page are the settings for Phones, Voicemail, Texts etc etc.
Go to the Voicemail and Texts page to turn off the forwarding there.
If you are tired of getting that annoying "Press 1 to accept this call" crap, Select "Calls" and then turn "Call Screening" off.
Like I said, Google is a cloud service. If you do not do this and you go get a new Android phone, these annoying traits will also occur on your new phone as well until you disable in your account settings. That is the magic of the cloud.
I hope this helps...it fixed it for me.