I am looking to advance my internal lead stuff and want to have a solid ESP with SMS integration. Currently using SendinBlue and it semi does what I need it to do but it doesn't have like really good tagging features like others have. What service are you using with ESP and SMS integrated that I can use a visual flow for the lead series?
I've been researching ESPs just a few weeks ago, in the end I went with mailerlite since I only needed basic functions and cheap pricing.
But anyways, while reading the reviews, https://www.mailjet.com/ was one of the most recommended ones, have you checked that one out? It should have very good API features so it should be possible to do more advanced stuff with this one.
Hey @ianternet.
I used to use a service called infusionsoft that is now called Keaps (https://keap.com/)
This is exactly what I was using for a guy I worked with when we were doing webinars and SMS email stuff. Pretty cool visual builder, timed events, change user email paths based on if they open or not, all kinds of hooks into Zapier, etc and SMS as well. I think maybe this is up your alley of what you are trying to do. Hope this helps you dude. 
I was checking out Mailjet but their confirmation email went to spam in Gmail... so that was already a bad sign for me....