How do I sync my calender with my husband's iphone when he has different icloud account?

This may work, ie. use one Apple ID for iCloud (sync calendar and contacts) and a different one for store purchases.

http://support.apple.com/en-us/HT204053

Use one Apple ID for iCloud and a different Apple ID for Store purchases

You can use different Apple IDs for iCloud and Store purchases and still get all of the benefits of iCloud.

iPhone, iPad, or iPod touch

1. When you first set up your device with iOS 5 or later, enter the Apple ID you want to use with iCloud. If you skipped the setup assistant, sign in to Settings > iCloud and enter the Apple ID you’d like to use with iCloud.
2. In Settings > iTunes and App Stores, sign in with the Apple ID you want to use for Store purchases. You might need to sign out first to change the Apple ID.

You both have to be using the same iCloud account to sync data such as contacts, calendar, etc.. You can select what you want to sync but you still need to use the same account.