Can anyone sumarize for me the Islamic story of Ishmael? Other than the suggestion that it was Ishmael rather than Issac that Abraham took to offer as a sacrifice, but God spared the child, what else is told of either of them in the Qur'an or the Hadith?

Several times, from several different posters, I have heard Muslims express concern that Ishmael was the first-born son and therefore......What?
....I haven't been really able to tell what it is that people are trying to say rightfully falls to Ishmael other than the privileges of being the recognized first-born son. I know of no Jew or Christian that disputes that Ishmael was Abraham's oldest son.

The covenant that Jews and Christians speak of God making with Abraham has nothing to do with being the first-born, but of being the child that God promised to Abraham that he would have through Sarah. So what is the point of Ishmael being the first-born? What is changed by recognizing that?