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.
“Thanks for calling the desk of (insert your name) at (insert your company name). I’m either on a call or away from my desk but if you leave your name, phone number, and the reason for calling, I’ll return your call as soon as possible. Thank You.”

There is nothing more frustrating than being given an alternative contact number and then not having enough time to note the details.
Make sure you keep your promises too. If you want to specify a time (which you should) ensure you get back to the customer within the timeframe.