Hi Amy,
I recently faced a similar issue that we got around by using an API to connect Infusionsoft to a system that could send texts.
It’s all a little complicated and you might not have another system like that available though. If the texts are fairly infrequent, you could do them manually by setting them up as tasks. Include all the text you want to send in the text message, including merge fields, into a task description and set the task to send a notification to the user who will send the text when the task is triggered.
Then just copy and paste the text from the email to your text message conversation with that contact.
This might not be a long-term solution and may only work for small volumes of people (since it takes up your valuable time), but it could also be seen as good for client relations if you can personalise the text and reply right away.
If you go down the API route in the future, using a service like Zapier might be of use to you. I think sending text messages is a sorely missed feature on Infusionsoft and I would expect it to be implemented eventually.
Fingers crossed. 
Thanks,
Joe