Is saying "There is no god but Allah," then the other party responds with "Muhammad is the Messenger of Allah" at the end of phone calls or while traveling considered an innovation (bid'ah)?

Allah Almighty has commanded us to remember Him frequently in every state, and He has praised those who remember Him in all their circumstances, just as the Prophet used to remember Allah at all times. The word of sincerity, "There is no god but Allah, Muhammad is the Messenger of Allah," is one of the greatest forms of remembrance. The Sunnah upon parting is for a Muslim to say to his brother, "I entrust to Allah your religion, your trust, and the ends of your deeds." It has not been reported that the Prophet used to say "La ilaha illa Allah" upon parting. Abandoning this act of worship is following the Sunnah, and doing it may be an innovation, unless the intention behind it is to enjoin the word of monotheism and remind of its importance.