Hello @isaacb89 ,
The addon's pricing will depend on how many messages you anticipate sending to your SMS contacts. For example, if you have 100 SMS contacts, but anticipate sending at least two 160-or-less character messages per week, plus wanting to account for automated replies, then you'd likely want to look at the 501-1000 tier. SMS Marketing
I'd recommend going through this article, which covers the SMS addon's pricing structure, as well as other elements related to adding it to your account.
See also:
Getting started with SMS (PDF download)
Registering your account for SMS
SMS marketing overview
SMS marketing best practices
SMS marketing while respecting quiet hours
Enabling SMS for landing page sign up forms
Importing SMS contacts list
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