Even an open-source client is hard to trust as a native install in your mobile OS. Sooo many ways your phone is insecure...
Since the baseband processor is a major attack point on a mobile device, it's a big deal that Wire does not need a phone number. It means you can use a WiFi-only device like an iPod Touch or non-cellular tablet.
In the bigger picture, we have to stop supporting companies whose business model is based on data harvesting. Wire is a small step in the right direction. We need more steps and more alternatives.