In Australian English it’s pronounced with the vowel /a:/ like in ‘part’. Problems arise when people use the /ʌ/ vowel (like in ‘up’) instead of /æ/ or /a:/. If you do this is will sound like the worst swear word in English. Many non-native speakers often pronounce the vowel /æ/ more like /ʌ/ because they don’t have a vowel like /æ/ in their first language. Many speakers of European languages will do this (Spanish speakers and Italian speakers) and also speakers of Japanese and Korean. This problem with /æ/ also means that if you say the word ‘back’ in your voicemail greeting sample, you are likely to pronounce it more like ‘buck’. remember to pronounce word endings in English. Check you aren’t dropping any endings off or mispronouncing them.
A word of warning: These greetings will not do you any favors if you're in the midst of a job hunt or work in a conservative industry. Always remember your target personas. If there's a chance they won't appreciate your sense of humor, opt for a straightforward greeting instead.

I like to say my phone number very early so the person can hear it again quickly by starting the message over and does not have to listen to your entire message again to hear the number. But do repeat your telephone number at the end of the message at least once and speak very s-l-o-w-l-y so the person can write it down as they listen. If you don't get a response to your first voicemail, don't hesitate to record a similar message once a week for two or three weeks. This sounds a bit excessive, but my experience has been that if there is even the slightest chance of meeting someone now or even in the near future, this kind of message will get their attention.
In an email, you may end by telling the contact what you want them to do next. In a voicemail, though, ending with something like, “Call me back,” or, “If I don’t hear from you, I’ll call next week,” can discourage the person from responding.