For any user that's trying to install the package under Ubuntu by instructions from official manual, please make sure that you also read setup manual from github page, section [C] and [D]
https://github.com/OpenSIPS/opensips/blob/master/INSTALL
I've tried to do a fresh setup of opensips on a virtual machine to test the functions. The provided packages on Jessie branch of Debian (which is supported by Ubuntu 14.04) is not included MySQL database deployment.
For a quick test I'm using the DBText as DB engine, and using command to add user will not succeed. Because the DBText engine requires email field, however the opensipsctl interface doesn't understand, so we should add some subscribers by adding some lines to Subscriber table, basically is located under path /usr/local/etc/opensips/dbtext, e.g:
1:brian:192.168.186.129:password:123456:xxx:xxx:xxx
2:julia:192.168.186.129:password:123456:xxx:xxx:xxx
Example above using the ip which is the virtual machine ip.
Good luck.