What voicemail system? This is not possible in the embedded VM or Express Messenger, but I believe a Welcome Message is possible with Nupoint or Innline 2020 voicemail for guests, *IF* they are using PMS integration which checks mailboxes in and out automatically. Otherwise, no...
Is this still a franchise "requirement" for some chains? I remember back in the late 90's and early 2000's some chains had a welcome greeting requirement so that every time a guest checked in, they would get a welcome greeting in their mailbox at check-in like "Thank you for staying with (blah, blah), be sure to stop by the bar and tie on a good one, then get a greasy over-cooked breakfast in our 1 star restaurant we like to call a 5 star in the morning. We just cleaned the pool because someone got sick in it yesterday, so make sure you shower afterwards so your skin doesn't fall off"... or something to that effect, but with the proliferation of cell phones no one even looks at room phones anymore and often a blinking light phone just get's unplugged. Most chains figured out fast this was too difficult/expensive for most properties to implement and no one bothered to listen anyway so this faded away as quickly as it came up. It's been probably 15 years since I have heard this request...