Microsoft Exchange Email Account Migration x 3

Our company requires assistance in migrating 3 x Microsoft Exchange email accounts from one hosted exchange provider to another (Fasthosts). We will need to ensure that all existing data is backed up safely and the email addresses transferred to new hosting with minimal downtime. We then need the new accounts to be set up properly in Microsoft Outlook and configured to push email to iPhones. We will also need a variety of \'catch-all\' email addresses relating to domain names owned by the company to be routed to one of the Exchange accounts.
It may useful for the freelancer to be able to access pc\'s remotely as our staff work from out of office locations, but this is not essential.
This is a business critical activity so we would prefer to work with someone who has significant experience in this type of activity.