afromobile,

Probably, I still do not understand your question.

If you need to call one module from another , just add reference to DLL to the called project.

You can “use WAP User Control Libraries from Web Site Project” .

Have a look to "Using Web Application Project(WAP) for development of DotNetNuke modules with Edit and Continue Support" post and Vladan’s BlankModule solution and in particular HowTo: Use DNN User controls with your modules.

Hope this helps.

afromobile,

If you are following sbwalker's  DotNetNuke 4.0.0 Starter Kit and Templates  post, you are using WSP, not WAP projects. Actually the DLL can be created, as it is described in his post last part(Module Architecture), but the procedure is quite complicated. This is why WAP projects have benefits for module development.  
To develop modules under WSP look at Michael Washington's posts : Super Fast and Super Easy DotNetNuke Module Development with Version 4.3 and DotNetNuke Module Development and the new Web Application Projects