i'm learning arabic at the moment! and i am far from muslim...
of course there are a number of arab speaking christian communities around the world.. the marionites of lebanon and syria, assyrians in iraq, copts in egypt speak arabic as their everyday language and there's somewhere around 10 million of them. then there's christian arabs in syia, palestine, israel, and other countries across the middle east... most arent ethnic arabs, but arab speaking people of other ethnicity..
then historically there are a sizeable number of christian arab communities - the ghassanids of syria who were a world power in their own right at times... the people of socotra off the south coast of the arabian peninsula were christian as late as the portugese occupation in the 16th century are a couple of example of ethnic arabs being christian...