Ok here it is!
Download this file and extract the phone.apk located inside:
Hotfile.com: One click file hosting: Evo On Boost Voicemail Fix.zip
or
Hotfile.com: One click file hosting: Evo On Boost Voicemail Fix.zip
THIS WILL ONLY WORK ON AN EVO 4G NOT 3D. YOU MUST BE ROOTED AND RUNNING GINGERBREAD!
Make sure your EVO is rooted.
Boot your phone into recovery mode by pressing the volume down key and power key. Once in recovery mode mount /system.
Download Android ADK from this link:
Android SDK | Android Developers
During installation change the directory for installation to c:\Android.
After the install run the SDK Manager. You will be prompted for downloads. Only check "Android-SDK-Platform Tools" and uncheck the rest.
Once installed you will be prompted to run ADB. Click yes.
Compy the phone.apk for voicemail fix to c:\Anroid\Platform-tools
Open command prompt and type:
cd c:\Android\Platorm-tools
If you haven't already deleted the phone.apk type the following:
adb shell
cd /sysstem/app
rm /system/app
rm phone.apk
rm phone.odex
rm vtt-sprint_v5_1_60.apk
exit
Once the phone.apk is removed you are ready to copy the new file over. Type the folling:
adb push Phone.apk /system/app/Phone.apk
adb reboot
Once phone reboots you are done!