..via AT&T's HSDPA network shouldn't be done. In actuality, it sends a voice file to whomever on the recieving end, not a voice message. (if you don't have a data plan eg: MediaNet, the 0.01$/KB adds up. And this won't guarantee the recipient will be able to listen to it either (for example sending from AT&T to Verizon phones).
Looks like the only way around this is to actually call up your voicemail number and leaving a voice message through a few teleprompts.
I was wondering if there's any workarounds to this, other than sending via AT&T to AT&T..