You cannot "Call" a module. A module is a container that holds subroutines/functions.
If you have a button on a main form and you want to display a message box with the value of a control on a sub form, you would use something like
Code:
Public Sub ButtonName1_Click()
MsgBox Me!Subform1.Form!ControlName
End Sub
where "ME!" refers to the main form, "Subform1" refers to the name of the sub form container (the sub form control name) and "ControlName" is the name of the control that you want to see the value.
or
Code:
Sub Test_Click() '<<-- button name
Call GetValue("frmJobs", "sfPay", "JobID") '(main form name, sub form name, control name)
End Sub
Sub GetValue(MF As String, SF As String, CN As String)
Dim sForm As String
sForm = "Forms!" & MF & "!" & SF & ".Form!" & CN
' Debug.Print sForm
MsgBox Eval(sForm)
End Sub
See Refer to Form and Subform properties and controls