"Hey Siri" will let you make speakerphone calls on iOS 8.3
Besides allowing Siri to make calls for you via the speakerphone on the your handset, iOS 8.3 will add support for CarPlay, additional emoji and the ability to log into Google accounts using two-factor authentication. Speculation has Apple adding its new music streaming service in iOS 8.4.
There is no word yet on when iOS 8.3 will be disseminated. Apple has started offering public access to iOS beta builds starting with iOS 8.3, so if you follow the directions, you might be able to load iOS 8.3 beta 3 on your iPhone. Keep in mind that since beta versions of the OS are not ready to be rolled out to the general public, certain features might not work. But that is the risk you take as a public beta tester.
source: 9to5Mac via RedmondPie