Ask for the complete specification.
Check the supported container and codec, sample rate, bit depth, channel count, maximum duration and file-size limit. Your system’s documentation or telephony partner should provide the required values. Different systems may expect different combinations.
Do not rely on the filename.
WAV is a container that can hold different audio encodings. Renaming an MP3 to WAV does not convert it. Mono and stereo, and different sample rates, are not interchangeable requirements. Compare the file’s actual properties with your system specification.
Keep a suitable production source.
Avoid repeatedly converting an already compressed file. Preserve the original production file and create the required telephony variant from it. When replacing an announcement, keep filenames and assignments organised so the correct message is imported into the correct step.
Listen after import.
Make a real call after uploading. Check volume, clipping, speech clarity, the start and end of the file and transitions into the next step. Test through the phone network, since a file that sounds good on headphones may behave differently in the target system.