word choice - What is the plural form of "SMS"?

What's the plural form of "SMS" (if X), like:

I'm concerned, I sent him over a million X but got no response.

I usually use text message to get rid of that situation.

Answer

The common way to pluralize acronyms is to add a lowercase S, so it would be SMSs. But SMS (short message service) is not usually used like that. SMS is the service you use to send text messages. SMS can also be used to talk about a feature-set ("It's got unlimited SMS."), or a technology ("This tablet supports SMS."). Both text (sometimes abbreviated txt) and text message are used.

I'm concerned. I sent him over a million texts, but got no response.

or

I'm concerned. I sent him over a million text messages, but got no response.

Google Ngram seems to support this: