You can add second ("secondary) iCloud account to your device by going to Settings>Mail,Contacts,Calendars>Add Account>iCloud and signing in with a different Apple ID. Synced data in this account will appear alongside your other iCloud data on your devices without needing to change accounts.
The secondary account, which you can share with others, is limited to syncing mail, contacts, calendars, reminders and notes. Document syncing (such as iWorks) is only supported in the primary account (your personal one). You could always use a service like Dropbox to share documents using a cloud service.
The other issue you may run into is that iCloud accounts are really designed for personal rather than business use, and you may exceed limits placed on mail (http://support.apple.com/kb/ht4863) and other synced data (http://support.apple.com/kb/HT4489).