No, SMS is the common denominator. Not every phone has email, but they all have SMS. (Change of perspective, the computer is no longer the preferred medium of communication.)
In office jobs the chances are everyone will have a work computer which they spend a large portion of the time sitting in front of but only a subset will have a work mobile* and most people probablly aren't going to want to give their personal mobile number out to all their collegues
And while a phone has the advantage of portability there is no way that it's a preferable device to a computer for viewing and entering large numbers of messages
And then there are the techical limitations, a sms is only 160 characters. Yes modern phones can chain messages but that drives up the cost and can only carry plain text.
For people who don't work in an office it is of course a different matter.
* Yes I know some landline phones support SMS but afaict it's the exception not the rule.