Hubspot has released an SMS add-on, which is great. They also have integrated this with the Inbox feature so you can respond to income SMS. Also great. I know it is a work in progress with more features in the works.
One thing that is very badly needed in my opinion: bounce processing for SMS. Currently, if someone explicitly opts in to SMS on a webform with a typoed or incorrect phone number, Hubspot continues to send SMS to them even if the messages are rejected from the carrier. The process for manually unsubscribing these contacts is extremly time consuming. The result is that you waste some of your SMS sends on bad s and it is undoubtedly bad for your sender reputation.
If the add-on could be built out further to accomodate this, it would be much appreciated.