I sometimes would rather send a message to my mother then call her simply because she loves to chat! Dont get me wrong as i love her to pieces but i am not a chatting type of a guy most days and sending a message just seems to work for me a little better.
I did it with my cell phone once, i sent a recorded message through the voicemail to a Telus client. Although it is the same company, I am guessing that it is possible as it asks you for the recipients mobile number.... So it should work! Go through your voicemail options!