If you are not able to phone me, there can be several reasons:
the number is inaccessible because I am in a place which the radio signals cannot reach, such as some large buildings, the basements of car parks, the subway, ecc. In this case just wait and try later. There will usually be a message saying that my telephone is temporaly inaccessible
i sometimes switch off my mobile phone because I don't wish to be contacted for the moment
you have dialed the wrong international access code. My number is italian and you have to dial first 00 (international access code) and then the code of the country (which varies according to the country you are in, 39 for Italy). My number is
+39.393 300 91 61
from a foreign country. Note: don't leave a message on the voice mail. I listen to it very rarely. Use an e-mail to send your message.