Hi..

Unit testing and  Integration testings are the phases of
White box testing later that we are moving for manual
testing i.e nothing but System testing,UAT
testing,Performance testing etc.

In integration testing mainly we are concentration on the
joining of the two modules and following are the 3 types of
white box testing techniques we have to follow

1)Top-Down Technique
2)Bottom-Up Technique
3)Hybrid Technique

In top down technique we have  to integrate main module and
some of the sub module replaced by stubs which are in under
construction like

               main module
                   / \
                  /   \
              (Stub)  (Stub)
               Sub1     sub2

In bottom up approach we have some of th sub modules and
main module which is in under construction replaced by skel
as follows
                Main module
                   (skel)
                    /   \
                   /     \
                  Sub1   Sub2
And the last and final approach is Hybrid Technique
Means in this we need to integrate main module and sub
modules which might be in under construction as follows
                   Main module
                   (skel)
                    /   \
                   /     \
                  Sub1   Sub2
                (stub1)   (stub2)

Integration testing is neither a black box nor a white box,
it is the combination of both black box and white box, so
integration testing is a Grey Box testing. This is why because
During integration testing we will be doing 3 types of
testing techniques
1. Top -Down testing
2. Bottom-up Testing
3. Sandwich testing/ Hybrid testing

Actually these are black box techniques but there are
conditions where some modules are not done before hand and
we need to test so we take the help from developers to
develop a small peace of program which is called stud and
driver. Using these we can make connectivity to unmade
modules and move forward to other module.

 So we need both coding part as well as black box technique
part that is the reason it is called as Grey box testing.

Still we can go indepth related to integration later but as
of your question it is Grey Box testing.

Integration testing is black box testing because in 
integration testing we are only concern about interaction 
between submodules (r integrated modules are working as 
specified) .We are not bothered about how it works?