The version of my AGEphone does not run hot, but it still won't ring.
My phone uses MS Live push mail, so it is always connected.
Yes, AGEPhone's sound quality is not so good compared to PortSiP. You need to increase the outboud buffer size to 80 ms or even 120 ms. On PortSIP, even GSM sounds decent.
I wish the next version of PortSIP will offer an option to turn off the NAT keep alive.