Telecom companies like AT&T aren't providing "essential service". Being able to call/text someone is not a "essential service". Yet they are not supposed to ban people because they are merely the carrier.
...according to Title II, yes, they absolutely are.
The phone company is required to serve you even if they disagree with you not because of some high-minded ideas about free speech, but because it’s considered really important for people to have phone service.