Recently we helped a new customer combine their existing webmail accounts from Yahoo and Gmail into one Free Google Apps Standard account that could send from their domain name. The merger involved transfering 4 Gigabytes of Email and 1700 Contacts from Yahoo and as well another 600mb of Email from their gmail account.
We used the migration tools from https://www.yippiemove.com which copied over the 4 Gigabytes of email via the "cloud" in under 2 hours. We used the export CSV Tool for the contacts and the Gmail Backup and Restore tool to migrate the Gmail Emails. The custuomer has now consolidated all their accounts into a free Google Apps Standard account which is valid for up to 10 users.
Let us know if we can help you out with any cloud migration problems or questions!