One more thing is that SMSes can be buffered by the core network and sent when the control channels are free enough. So, the effective volume of SMSes that could be handled at any given time can be much larger than voice calls, which have real-time channel requirements.
You can notice the delay in message reception due to buffering on occasions such as New Year eve, if you've texting from a populous area.
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I've heard one too: "two protons walked into a black hole..."
One more thing is that SMSes can be buffered by the core network and sent when the control channels are free enough. So, the effective volume of SMSes that could be handled at any given time can be much larger than voice calls, which have real-time channel requirements. You can notice the delay in message reception due to buffering on occasions such as New Year eve, if you've texting from a populous area.