I'm getting a lot of voicemails I think it's spam

[dwhite]

These voicemales are from an unknown source so I wouldn't open them anyway, I'd like to filter any unknown or withheld id email, anyone know how these come to my Kmail account.

[doktor5000]

Voicemails to your email account? You sound confused ...

Anyways, if those are spam mails, they are usually sent to you via the BCC function (blind carbon copy).
So set up a filter for To, CC and BCC fields on "undisclosed-recipients" - although that may yield a lot of false positives.