Nothing significcant, they are interchangable names for the same religion.
And what religion did decendents of Ishmael? follow before Muhammed came along?
I beleive that "Allah" was the name of the pagan Moon God in Mohammad's day. When he started the Islam religion, Mohammad tried to make a religion that would be aceptable to the Allah worshipers, Jews and Christians alike. What he got was one that offended all three. That is why the Muslum religion was spread through violence, it was not accepted by any group at the time.