I've got one of these phones and I've been far from impressed. I still make regular use of my softphone. First problem is that the battery life is dreadful. You'll be lucky to get a day out of it (normal use) without a recharge. To make it usable you need to plug it in every time you get a chance.
I also have connection problems all the time - even with my own wireless AP. Maybe this is a general problem with all WiFi phones, or just with the DPH - I've no experience with other models. I tried getting it to work with port forwarding on my router, but this didn't work. So, I use a STUN server. Now, many this is the weak link - who knows - but whatever the reason the utility of the kit is low. When the WiFi phone can't make a call, I just boot up the softphone and make the call - so it's never the VoIP provider - it's either the phone or the STUN server.
In addition, I don't think I've every managed to make a call via a public WiFi AP - even though my laptop can connect with no problems.
So, I'd pretty much look for another model, or wait until the technology improves in general.