Issue with undefined function

I am having a problem calling a function. There seems to be two kinds of modules in my project. A) module that has functions that extend ci_model . These functions allow you to use this->. Typical CI stuff. B) module that is just straight php code. These functions don't extend the ci_model. 

I have a need to call a function in a A module from a B module. This won't work and I get an undefined function error when I run the call. What must I add to module B to tell it to look in Module A for the missing function?

I hope I explained this ok?

proof that an old dog can learn new tricks

You can implement your B module as library, put it in application/folder and load it in your A model, that extends CI_model

I think the original code was written to use php mail. Is there anything I need to do to enable php mail to work in my CI app?

proof that an old dog can learn new tricks

CI has email library, you can check it documentation