Setting up iCloud requires you use an Apple ID (email). Since there are other services included with iCloud, sharing an account could present problems. I guess you could turn off all of the other services, use a standard non-iCloud account, but then sync that Apple ID with Calendars.
I bet you could find a 3rd party app that might do the trick. I don't know of one off hand, but perhaps someone will jump in this thread and offer up a suggestion.
I have multiple calendars on my iPhone. I have a work, personal and there are calendars with gmail & hotmail. Perhaps you and your wife could share a gmail account and use the calendar only. I know this works between devices because I use an iPad in addition to my iPhone and all stays in sync.
Go to iCloud.com and enter the calendar section. On left side where it lists your calendars, you'll see a little circle "rss feed" type icon. Click on that and it will give you the option to share your calendar with a contact. You can either let the contact edit the calendar or just view it.
Once you've done that, Apple will send an email to your wife's .me account. She goes on her phone/pad/mac or what ever and follows the directions in the email. The iDevice will then automatically set up that calendar in her calendar app. And that's it. Anything you add will be added to her phone within 30 seconds.
You can also share a reminder list. My wife and I share a "shopping list" list and it works great too.