Two iPhones, one MacBook - sync/backup question

In regards to iTunes content, an iPhone can be synced with an iTunes library on a single computer only and photos can be transferred from a single computer only. When transferring iTunes content and photos from another computer, all iTunes content and photos transferred from a different computer will be erased from the iPhone first.

There is no device limit for the number of iPods, iPads, and iPhones that can be synced with the same iTunes library and iTunes account on the same computer. Each device can have its own sync preferences with iTunes and iTunes creates and maintains a backup for each device.

When syncing two iPhones with the Address Book and iCal under the same computer login account, the contacts and calendar events will be the same in the Address Book and iCal and on both devices. There is an option to sync select Address Book Groups and select calendars only with each iPhone, but the contacts and calendar events with both devices will be available in the Address Book and iCal.

If you want to keep contacts and calendar events completely separate, you need to create a computer login account for your wife. You can enable Fast User Switching to make the process of switching between multiple computer login accounts a fast and easy process. An iTunes library can be shared between multiple computer login accounts. Your iPhone's backup will be updated and stored under your computer login account, and your wife's iPhone backup will be update and stored under her computer login account.