You're misinformed about the channels that are used. It's actually the control channels that carry the SMS messages (the channels used for association to tower

You're misinformed about the channels that are used. It's actually the control channels that carry the SMS messages (the channels used for association to towers) not the voice channels. These channels can easily become heavily utilized with a large number of connected calls or devices associated to a single tower. Additionally, the message isn't dropped, it's instead queued for later delivery which typically occurs when your device migrates to a different tower.