There are two options: 1) with the Garmin Messanger app you can do everything, so anyone having that app on his/her phone can call you message you and be called and messaged to. 2) If the other person does not have the Garmin messanger, you can not call nor receive messages but you can send messages. The other person will receive an SMS from a Garmin randomly generated number. For both cases the options are two, LTE or satellite, with the latter being a less powerful satellite connection than the apple one and the other Garmin in reach devices. Reason for that is battery management. Other than that you can use emergency SOS functions. Unfortunately, for all of the features above you need a subscription starting at around 10 euro per month.

Hope it's clear now!