will siri dial a call on iphone 4?
No because Siri won't work at all on an iPhone 4.
Ipads don't make phone calls.
I have an iPhone, I was just posting this from my iPad
Yes, Siri can make phone calls for you on an iphone but, as has been said above, Siri is not available on the iPhone 4. It is available on the iPhone 4S and iPhone 5 as well as the iPad mini, iPad 3, iPad 4, and iPod Touch 5th gen.
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