The Voice Messenger or Speech 64 is a speech synthesizer cartridge for the Commodore 64.
The Voice Messenger cartridge uses the General Instruments SP0256-AL2 speech processor. The cartridge has its own memory and does not use the memory of the C64. The cartridge can be used without any special software.
This voice synthesizer is more sophisticated than the software only "Software Activated Mouth" (or SAM) because it was on a cartridge.