1) Click the downward facing triangle to bring up the properties window for the greeting.
2) Click Split Stereo to Mono.
1) Click the drop down menu for "Save as type".
2) Choose "Other uncompressed files".
3) Click Options.
Press OK to save changes.
(Note: after doing this once, the default for "Other uncompressed files" will be WAV U-Law, so you shouldn't need to repeat these steps again. You will however always need to split stereo to mono, kill one stream, and set project rate to 8000 before exporting).