An article titled "YourSay: Each one expresses 'God' in their own way" has an interesting perspective on the term "Allah" as used by Arabic-speaking Christians. The commenters are responding to an original letter suggesting that use of "Allah" by Catholics was offensive and that Methodists and others do not use the word.
Responders point out that differences in the word used for "God" varies worldwide due to native language, not religion or denomination. They also point to early use of "Allah" by people in the ancient world before the coming of Islam. The insistence that Christians not use the term "Allah" is an example of religious persecution of Christians in the modern world.
These are reasoned responses that lead me to wonder about some of the varied Christian viewpoints on Allah. Some hold that God and Allah refer to the same deity. Others insist that God and Allah cannot be the same. These people assert that the Koran and the Bible show two widely different deities.
Is it just possible that we fallible human beings have come to learn of and about God in different ways, through different means, and under different circumstances? If so, would it be so remarkable that each group of peoples would then have different views about God, Heaven, and so on? Since we are fallible, it's highly probably that no one group has the "complete" picture of God.
Perhaps if the proponents of God, Allah, and Yahweh were to approach each others' beliefs with that in mind, we could all work toward a common goal of doing God/Allah/Yahweh's work while we are here on earth.
God - Allah - Yahweh ... the three are one?