Which is correct, "voicemail box" or "voice mailbox"
Solution 1:
There are three types of compound nouns.
open or spaced - space between words (tennis shoe)
hyphenated - hyphen between words (six-pack)
closed or solid - no space or hyphen between words (bedroom)
Even though Wikipedia posted voice mail as a closed compound noun (still voice mail system is an open compound noun there) and you get more google hits for voicemail (18.1 million) than voice mail (9.9 million), this Ngram Viewer favors voice mail over voicemail. Also, another Ngram Viewer records more of voice mailbox or voice mail box than voicemail box.
As the two Ngram Viewers show, people started to use the words around year 1980 and as commented above, it is difficult to say which is correct. But, voice mailbox is the one which is favored.
Solution 2:
Between "voicemail box" and "voice mailbox", there's seems to be slight preference for the former, but definitely not enough that the latter can be considered incorrect.
I looked at the websites for several phone/voice companies and found:
- AT&T: voicemail box
- Mitel: voicemail box
- T-Mobile: voicemail box, mailbox
- Google Phone app: voice mailbox
- Xfinity: voice mailbox, mailbox
- Verizon (Voicemail FAQs, Retrieve Voicemail Messages, Hosted Voice Messaging Service (Voice-mail)): voicemail box, voice mailbox, voice-mail box, voicemail mailbox
- Microsoft: voicemail mailbox (but "mailbox" means email)
All of them use "voicemail" by itself also to refer to the box.
Note: The all-open spelling "voice mail box" seems to be predominantly used by the NY Times (and other US news sources), which Grammarist calls "editorially conservative". But Microsoft also has one instance of "voice mail" among their other instances of "voicemail", so there's not always consistency.