Exchange setup query

Hi Guys,
We have a situation with exchange set up and was wondering whether you guys can help?
Here is the scenario:
2 small companies company A and company B that reside in the same office space  currently have the following e-mail configuration.

Exchange Server A  ( 2003 Standard Edition)  running in the office equipment room. The Exchange Server A has full connectivity to an ISP.

Company B currently uses a hosted e-mail solution.

However the plan is for an Exchange Server to be introduced to serve Company B  and stop using the hosted solution. Exchange Server B  ( 2003 Standard Edition - although could be upgradeable to Exchange 2007 standard edition ) will not be run in an office but in a remote data centre in the same country.

Do you guys think that it would be possible to get these 2 exchange servers to work together?

The reason for this change is so

1.A user can retrieve historical e-mails at will from local back ups if required from both companies.

2.The same user can view calendars from both servers using one client ( Outlook ).

This user works  remotely or in the office.

Each company has its own e-mail  address convention i.e. firstname.lastname@companya.eu and firstnameinitial.lastname@comapnyb.com  

Is there a configuration that will achieve this functionality ?

Regard