I've recently had the pleasure to set up a new iPhone 5S for a friend of mine. I noticed that pretty early on during the on-device-setup it asked for your iCloud Apple ID (as you can see over at Ars..). Later on I discovered that using this Apple ID the system had pretty much tried to activate every service - so iMessage, Facetime, iCloud sync, Photo Stream etc. were all available relying on this Apple ID.I started to think about my multipe IDs and I wondered: Wouldn't it be cool to just have the one Apple ID and use it for all the services, thus having just one password? So I said: this is a nice little side-project.Because I use iTunes longer than I used mobileMe - I had a Gmail address as my Apple ID for the stores and I had a nice mobileMe (and later on corresponding iCloud address) for my Contacts-, Calendar- and Photo Stream Sync and for things like find my iPhone etc.Because most of my friends know the Gmail address, I used that one on Facetime and iMessage and so on.Now the two ID method should vanish and I just want to have one Apple ID on my phone.

Which ID to choose?

For me the decision was fairly easy. My Gmail address based Apple ID was easy to use when communicating with friends (iMessage / Facetime) plus all my purchases in Apple's digital stores are tied to that account - so I just had to pick my Gmail based Apple ID as the one and only ID.I also thought about what kind of data is really 100% set in my other iCloud Apple ID. This boils down to a couple of documents in the cloud (nothing to write home about) and to my Photo Stream of round about the last 1000 photos (but these pictures exist elsewhere i.e. in my iPhoto library). Thus I said to myself there would be no issue in turning off the mobileMe based Apple ID.

What to do?

I dug around the internet and found a neat guide. Essentially I had to log off iCloud but keep things like contacts etc. on my iPhone. I then turned on iCloud with my Gmail based Apple ID. Plus I had to repeat all these steps on all iDevices and Macs I own.Details with nice pictures are here:http://www.ilounge.com/index.php/articles/comments/transferring-data-when-moving-to-a-new-icloud-account/

What about email to the old iCloud / mobileMe addresses?

Well when I said I felt I can easily retire the mobileMe Apple ID - I should say it seemed feasible on the phone - but I definitely don't want to loose these nice Email addresses. So I decided to keep the old ID around. Plus I used the iCloud web-interface to set up a forward of all emails to the mobileMe address to my Gmail address. It's easy to do in Mail's preferences. Another idea would be to simply set up the mail account via SMTP in any kind of Email program if necessary. Instructions are here.

Summary..

If you do not love to have two IDs on the phone it is quite easy and straight forward to switch and use just one ID. You should beware and check where your purchases are linked to. iTunes in the Cloud is quite a neat feature allowing you to re-download apps etc. There are ways however to use Apps from several Apple IDs on one device the bad thing is then: should something happen to the device you cannot easily re-download the Apps from Apple.So for me it worked. It was quite quick. The main challenge is to turn iCloud off and on again with the right timing (keeping in mind i.e. that in that moment you should not change a contact on your Mac etc.) - so if you have lots of devices connected to the internet this might be a bit cumbersome.I unfortunately lost my Notes on the way (one possible reason could be that they are somehow tied to a SMTP folder in your iCloud email address). For me this was no big issue as I mainly use Simplenote and furthermore I was able to simply copy and paste the lost note via the Web Interface of my old mobileMe iCloud system.