Communicating with people of other religions is violation of the principle of al-Wala' Wa al-Bara' "loyalty and disavowal" in Islam.
Dealing with people of other religions and cooperating with them for purposes of common interest can never be prohibited in Islam, as Prophet Muhammad (PBUH) dealt and communicated with other people and never forbade Muslims from doing so. Allah says in the Holy Quran, "Allah does not forbid you from those who do not fight you because of religion and do not expel you from your homes - from being righteous toward them and acting justly toward them. Indeed, Allah loves those who act justly. Allah only forbids you from those who fight you because of religion and expel you from your homes and aid in your expulsion - [forbids] that you make allies of them. And whoever makes allies of them, then it is those who are the wrongdoers." (Al-Mumtahinah: 8-9).
Our religion does not command us to deal with others as enemies or deal with them rigidly except in case of defense. This approach is approved by all people of sound mind and common sense. However, if Muslims are in state of peace with others, then they should follow what the above quoted Glorious verse commands regarding being righteous, just and with good and kind treatment.