Can you talk on the iPhone and use Siri with Monster beats headphones? I want a set of Beats by Dre headphones and have seen that they come with a control on the cord. Does this have a Mic? and can it be used with Siri in the same way the official Apple ones can?

I have looked at online reviews etc, but little is mentioned with iPhone voice compatibility.
Yes.
The Monster Beats cables are fully compatible with Apple hardware. They have a mic to support voice actions and Siri. They also have all the hardware buttons for playing music and making phone calls.
I happen to own the Beats Solo headphones.  This is what the packaging says:

&quot;Made for iPod&quot;, &quot;Made for iPhone&quot; and &quot;Made for iPad&quot; mean that an
electronic accessory has been designed to connect specifically to
iPod, iPhone or iPad, respectively, and has been certified by the
developer to meet Apple performance standards.
(also see MiF logo on Apple's website)

These minimum standards would include voice and button actions using the headset.