The advantages are clear: asynchronous media are less intrusive and save time. The recent advances in technology make them appear as reliable as synchronous media. However, we still need recognize that even the best run asynchronous channels still cannot guarantee when or even if a message reaches its recipient: The internet connection is slow, the SMS relay between to mobile phone networks failed and the SMS gets simply dropped, the battery is empty.
When you want to ensure that your message reaches the recipient you must take extra care to ensure that it is fully understood by the parties. When using asynchronous media to provide outcome certainty I use double or even triple acknowledgement. Here is an example:
Me: "Would you like to go for dinner tonight?"
John: "Yes, what do you suggest?"
Me: "Lets meet at Starbucks Downtown at 19:30"
I cannot be sure if John has received my message and that our dinner is really on.
Now I know that John has received my previous message. Most people leave it at this and most of the time this is ok. However, John cannot be sure that I received his acknowledgement and that our dinner is really on.
With acknowledging a second time I let John know that I got his acceptance. This usually suffices.
In rare cases, like when roaming in different networks where SMS loss is more likely a triple acknowledgement might be warranted.
If in doubt most people will switch to a synchronous channel. When I do not get an acknowledgement from John and are about to leave for downtown I will grab the phone and call him:
"John, you haven't confirmed our dinner. Are we still on?"
But John might be in a meeting, out of reception or does not hear his phone ring. Multiple acknowledgements prevents last minute corrections and hectic.
When you do acknowledgements be careful not to add any new information like "Ok, are you ok with shifting to 20:00?". You will need to start the multiple acknowledgement again.