Messages will be sent along with the token transactions. For example, the minimum transaction cost is set to 0.00001 MMC - this is 0.0025 cents at the current exchange rate. When you send a message your balance is reduced by this amount, and when you send messages, your balance increases.
Even if you do not receive messages, but only send them, 1 GMC worth 2.5 $ is enough for 100 000 messages. Yes, if you send 300 messages a day and do not receive a single one, you will have enough for 1 year.
But after all, the GMC can not buy but mine ...