Emails triggered by milestones, like anniversaries and birthdays, are fun to get -- who doesn't like to celebrate a special occasion? The beauty of anniversary emails, in particular, is that they don't require subscribers to input any extra data, and they can work for a variety of senders. Plus, the timeframe can be modified based on the business model.
"Segmentation tactics are going to take a big step forward in 2020 as modelling based on recency, frequency, and monetary value becomes easier for brands to embrace. Some marketers are embracing it to better manage their engagement rates and improve their deliverability rates, especially at Gmail. Others will embrace it to better match email frequency to engagement levels and to maximize customer value. More segments and more dynamic segmentation is the future of targeting."
Check out Pure360 – from their website it seems like they have both SMS services and integration with Salesforce. I can’t vouch for their service as I’ve never used it, although I did used to live about two minutes from their offices in Brighton! The other option would be something like Infusionsoft. I’m pretty certain that they have SMS functionality, and would be very surprised if they didn’t integrate with Salesforce.