Spam and other unwanted calls might not get through to your phone if you use a program called AT&T Call Protect. Any AT&T customer with an iPhone 6 or later running iOS and able to handle HD voice conversations can download the software. You can switch to the premium model for free or use the freemium model. Either way, you can block unknown numbers and get alerts when they try to get in touch. This is an advanced method of no caller id.