Apple updated its iPhone software development kit on Wednesday to allow Internet telephony apps to work on the 3G network. The little-noticed move effectively unlocked the ability for the iPhone — and the upcoming iPad — to be used as Web phones.

Because the iPad includes a microphone and will run iPhone apps, that means the tablet will gain Internet telephony, too.

iCall, a voice-over-Internet Protocol (VOIP) calling company, couldn’t be happier. The company promptly released an update to its iPhone app today, adding the 3G support.

Arlo Gilbert, CEO of iCall, wrote on his company’s blog this week: “Yes, believe it or not … the moment that we have been eagerly awaiting has arrived and we are proud to finally say that iCall for the iPhone is fully functional over 3G networks.

“We have thoroughly tested the voice quality over 3G and it exceeds even our expectations … so now anywhere where you have a 3G data network you can make free phone calls.

“Existing users do not need to upgrade, the 3G block was a server side block on our end and it has now been removed. If you are using version 1.2.5 or newer of iCall for the iPhone then just restart iCall while on a 3G network and enjoy calling.

“The only caveat here is that AT&T’s 3G network is overloaded big time and call quality will depend upon the 3G signal you are able to get.”

Good luck with that.