When a message containing emoji is sent to a 1s2u Virtual Number, the callback will show these characters in hexadecimal values.
Example: %F0%9F%98%84%F0%9F%98%83%F0%9F%98%80%F0%9F%98%8A%F0%9F%98%98
If you need help decoding these characters, there are some useful tools online such as http://www.url-encode-decode.com