Vocaroo was the tool that I usually used to record those voice messages. When you record on Vocaroo (registration not required) you can talk for a few minutes then share your message by embedding it into a blog post, giving someone the link to it, or by printing a QR code that people can scan to hear your message on their phones. A demonstration of how to use Vocaroo can be found here.
If you don't have a classroom blog, you might want to explore sending messages to students and parents through Remind. Remind is a free service that you can use to send text messages. A few months ago Remind launched the option to distribute voice messages to students and parents. It's a nice option, but your voice messages are limited to 15 seconds. If you use Vocaroo you can record and share longer messages. Record your message on Vocaroo, grab the link to it and post it in a Remind message with directions to click the link. Students and parents who smartphones (and some feature phones) will be able to listen to your voice recording.