I don't work with CXP, but if you create several DLLs containing different functionalities, functions from those DLLs are published to other DLLs by including their LIB files. So, if you have a DLL containing your customer registration called "CUST.DLL", publishing functions from this DLL to others ...
LbClick (and others, like LbDblClick, LbDown and the same for right clicks) are callbacks available with any part that is based on a XbpStatic, and the parts (heading, dataarea, footer) of a column are statics. You may also use this slot on text statics and elsewhere, like this: @ 1,1 DCSAY 'Hello' ...
Most providers (Verizon aswell) have a REST API to send short messages. In most of the cases, the authentication is done using the header parameters, and the message itself and the recipient(s) are added as normal parameters. We do this with Xb2.Net, but it's almost the same with the http-functions ...