MAJOR SPOILERS
TFMH18 writes, "I am pretty certain it is meant to be Beth, some time in the future, calling Josh, therefore letting the audience know that they end up together in that storyline as well."
I LOVE this idea. I left the performance (one of the last in DC) sobbing my eyes out about Josh's death, although I saw it coming when he said they always put the doctors in the rear -- not near the combat. I very much like thinking that Josh and Beth create a permanent life together, and that Beth has gained the maturity to handle a Liz-like timeline.
End of spoilers
I always thought the names Liz and Beth should be reversed. To me, Beth sounds like a homebody's name. Liz sounds like a tough, high-powered professional.
Audrey, the Phantom Phanatic, who nonetheless would rather be Jean Valjean, who knew how to make lemonade out of lemons.