I'm working on a plugin for Twilio to replace (at least for me) the Google Voice SMS plugin. Why? Because the GV plugin is pretty fragile. It works by screen-scraping the GV web interface, and is prone to breaking anytime Google changes anything on that page. Also, the developer of that plugin is no longer actively maintaining it, so fixes are pretty sparse. And I only have one GV number and if I want to use it for anything else, I can't use it for the plugin.
So, Twilio. Yes, it's a pay service, rather than free like GV. That doesn't bother me if I think it's worth what it costs. And it doesn't really cost much. For a local (not toll free) number, it's $1/month in the US. And $0.0075 (less than 1 cent) per SMS. For my usage, I'll rarely go much over $2/mo.
Also, they have a very well developed API with libraries for lots of languages.
And, they have voice services as well. So you can pre-record a message (or use a TTS solution that creates an mp3 file on a server), and have Twilio call someone and play the message. Included in the monthly number cost, and outgoing calls are only $0.015/min.
I've got basic SMS sending working now, and receiving is mostly working. They archive all SMS messages, in and out, so I have to filter for incoming messages still.
I'm posting this in advance so that you can get a Twilio account set up in advance. They do have trial accounts you could use, but you don't have as much control over them as a paid account. Probably good enough for trying the plugin out, anyway. To set up the plugin, you'll need a Twilio phone number (you can have more than one), plus the SID and Token for your account.
Depending on big stomping on other plugins, expect something usable in a couple days.