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.
If they are calling without an expectation that you always pick up (such as if you are a business coach or a one-man shop) then thanking them for calling might make the most sense.

Hi, you have reached …. Please leave your name, phone number and a message and if we like it we will return your call.
2. Mention Hours of Operation Upfront. Most callers expect their call to be answered. Once they realize that your office is currently closed, the most important piece of information they probably want to know is your standard business hours.