I don't have a problem with it/do it all the time. In fact it's actually a pretty good strategy if the church's portal is modded the correct way (similar to a portal you can hit from your home or work.) Besides if the church is doing that "text the sermon giver questions to answer after the sermon" thing that week tons of other people will be playing with their phones anyway.
Since the churches I go to are all small enough that people can actually speak to the pastor in person, there aren't tons of other people will be playing with their phones anyway. In fact, there aren't tons of other people, period.