How to recover lost contacts on iPhone 4?

I switched numbers (and data) between an iPhone 4 and iPhone 5 recently, and some of the contacts in the iPhone 5 got lost in the process (I was trying to put them in the iPhone 4); is there any way to retrieve those contacts? I thought I backed up the stuff in iCloud.

Do not worry much about that.
and use a professional iPhone Data Recovery tool to get back the iPhone files.
The one I use is Hodo iPhone 4 Data Recovery software which is able to recover almost any iphone files including photos, videos, notes, contacts and more.
What you need to pay attention is: DO NOT add any files into your iPhone before recovery is done.

I've just met the same problem with you, and iPubsoft helped me recover my lost iPhone contacts conveniently!

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