Using your iPad to make phone calls might seem a little awkward given its size, but on speakerphone, it actually can be pretty effective if you know what to do. As long as you have a WiFi or 3G connection, a free app can turn your iPad into a telephone with its own number, and you can even have it roll missed calls over to your cell phone should you choose to do that. This is the best iPad phone integration job we’ve seen yet – and it’s free. Even the occasional ads aren’t really annoying like you might expect they’d be.

After downloading the Whistle app on your iPad (also available for your iPhone if you’re looking for a second number or want to save on minutes), set up a free Whistle account. They’ll assign you a number, and there’s some flexibility in choosing what your number will be. Want a new area code? Here’s your chance to pick.

Turning your iPad into a phone with Whistle is easy. After you’ve got your number, hit the Contacts button inside the app to start dialing up your friends on your sneaky new number. If you use Whistle at a corporate level, you can see other users on your network as well and initiate instant conversation with them. You can have two calls at once (with one on hold, of course) and you have the ability to merge two calls together – a huge bonus.

Once you’re on a call, the voice clarity is quite good. We tested by calling contacts using landlines, AT&T and Verizon cell phones, and our own iPhone. All were very clear, and to be honest, the codec used for voice compression on Whistle sounds better in some cases than when we use our standard iPhone to make cellular network calls. Even with the iPad turned into a speakerphone, there was very little, if any, feedback.

Check out the video below to see an incoming call and how it works:

We definitely recommend Whistle. It’s free, it works incredibly well, you get your own phone number, and it turns your iPad into a phone. What more can you ask for? Just grab it.