Office 365 and Inhouse Exchange ..

We have a scenario here.

1. Company 1:

Exchange /AD : In-house

Lync Server: Office 365

1. Company 2:

Exchange / Lync: Office 365

With some kind of Sync on Office 365, they can see each other on Lync. However, they can’t see each other on Exchange and hence cant lookup in GAL or Calendars.

Requirement is to sync Exchange (between in house Exchange and office 365). They are  entirely two different Organizations and merger is in progress.

What can be the best solution here? They already have a Federation server running to sync the Lync users.

Raj