helenthomo Having the same problem. Switched to a new iPhone yesterday and calls going straight to voicemail but am able to call out. Have tried all suggested fixes.
There have been several reports of this problem, and it is currently under investigation. In the meantime, try switching your phone off and on a few times. Check for network equipment problems by putting your postcode into the Network status checker here:
Try switching your phone form 4G to 3G.
For more information, see this thread in the Service Updates forum: