What does ban mean in text messaging?

See the Urban Dictionary related link. It depends on context. If it does not make sense as a verb. To ban is to prohibit. It may be possible to ban (prohibit or block) certain phone numbers from texting to your phone. Or somebody could decide to ban your phone number from texting to them. There is also an acronym for the letters B A N, which could be the meaning if the other meaning does not make sense. I won't repeat here, as it's derogatory, but refer to the related link.