m2m stands for mobile to mobile. if you have a text plan that covers your usage, m2m text would be considered free text messaging between verizon wireless phones specifically. domestic text is your standard outside of network text message. these are billed usage, unless covered by a text plan.
$5 text pack - 250 messages a month, whether incoming or outgoing, total
$10 text pack - 500 messages a month, unlimited verizon to verizon texting
$15 text pack - 1500 messages a month, unlimited verizon to verizon texting
i hope this helps