The Simple Network Paging Protocol (SNPP) allows sending a message through the Internet to a Pager (pager radio frequencies are more effective than cellphone radio frequencies at passing through walls). Below are addresses for various free publicly open SNPP message delivery servers (the pager you are sending the message to must be a subscriber on the applicable system). Just copy & paste the full address into your SNPP client.
[IANA Port assignment = 444]

SNPP Delivery Servers