I looked up MMS and it said :
MMS
Multimedia Messaging Service
MMS is a descendant of SMS (Short Messaging Service). MMS extends text messaging to include longer text, graphics, photos, audio clips, video clips, or any combination of the above, within certain size limits.
MMS is frequently used to send photos and videos from camera phones to other MMS phones or email accounts. Most camera phones have MMS, but many non-camera phones have it as well.
Many newer MMS phones also support SMIL, which allows various parts of an MMS message to be arranged into a small multimedia "slideshow" to be viewed on another SMIL-capable MMS phone.
See: SMIL
See: SMS
I will speak to her later today ot tomorrow and find out the model of her phone.
As to what type of voice file, I would have to see what kind I can record with the varried programs I have, but I get your drift on what it all depends on.