Shahada

I was talking to a Christian friend about mutual topics of interest. One of them is the definition of "Muslim" and its relationship to saying the Shahada. This friend brought up an interesting point: a Muslim is literally "one who submits to God." Likewise, a translation of the Shahada says: "There is no god but Allah ["the God"], and Muhammad is the messenger of Allah." This friend noted that a Christian, who believes that there is only one God, can say that he or she is a Muslim - one who submits oneself to God. In a similar, but fundamentally opposite, way, a Christian can say that "there is no god [lower-case G - an imitator] but Allah [meaning the Muslim deity], and Muhammad is the messenger of Allah."

Lest Muslim or Christian readers find this blasphemous or take offense, let me only say that I have given this much thought as well. I respect this friend very much and would like your opinions and help on this topic. Tell me what you think - if what or whom a person believes in is all-important, can a Christian legitimately say the Shahada and be a Muslim (in the literal sense) without committing blasphemy?