Since at least lunchtime on Friday, I haven't been able to receive text messages from people who are on the Optus network, but can from Telstra and Vodafone. I've tested this across a number of people. I have a Pixel 4a. I haven't been able to find anything online about this kind of problem, but I've tried generic solutions like restarting phone, checking for updates, even installed a different text app to check it wasn't a problem with the phone's default one. I am looking into switching providers because of this issue.