If the person you're trying to call or text has their phone powered off completely, your call or text message will not go through. When a phone is powered off, it is essentially disconnected from the network, and any incoming calls or messages will not reach it until it is powered back on.
Similarly, if you initiate a FaceTime call to someone whose phone is powered off, it will not ring on their end. FaceTime requires an active internet connection and a powered-on device to receive incoming calls.
If someone has powered off their phone completely, it may be difficult for you to determine this without any additional information. When you call their number, it will typically go straight to voicemail. However, it's important to note that there could be other reasons why a call goes to voicemail, such as poor signal or the recipient manually rejecting the call.