Are you streaming any other audio/video on your home internet connection while using Wi-Fi Calling? If so test it without.
I actually had this same issue with my Amaze. It ended up being a quality of service (QoS) issue with my ISP. Here is a site you can test your connection with (from a computer):
To test the connection:
- Click on North America
- Click the tack closest to your geographical location
- Once the java window loads click on "Click to start test" in the upper left
The results will give you download speed, upload speed (both need to be 256 kbps or above), and QoS (needs to be 85% or higher). If the QoS is below 85% try rebooting your modem and router the retest. If it is still below 85% you will need to contact your ISP.
In my case my QoS 52%. My ISP submitted some sort of work order and within a few days it was at 96-98% and my Wi-Fi Calling sounded much better.
It may also be related to packet loss or jitter which can also be tested from the above site. After running the QoS test on the right side of the screen click on the VOIP link. Jitter should be less than 10ms and packet loss less than 1%.
You're not going to like the answer... In short, the Amaze absolutely sucks at wifi anything. For most things, the user is unaware of just how poor (inconsistent) the wifi radio is. I have exactly the same problem with my Amaze (and my wife's Amaze). When I first got the phone, I asked for help here: http://support.t-mobile.com/thread/16463
And, while I went back and forth on the issue, to this day, I have no consistency or reliability with wifi. My wifes seemed to be better, but when her speaker blew, and I had the phone replaced, the new one is equally as bad as mine.
I tried everything. I even upgraded my home wifi to a corporate/enterprise level access point that is strong enough to provide power to my other wifi devices half way down my street. But the Amaze, only works marginally.
In the end, my work around was to port my number to Google Voice, and then use an OBi110 box to pipe the GV calls to my home phone system (I do not have a land line). Now when someone calls my cell phone, they're really calling my GV account - which forwards the call to my cell and the OBi box - which rings all the phones in my house.
I keep wifi calling off. I don't miss any calls, and the best part is, even if my phone has no service, or the battery died, my home phones still ring.
It's drastic, but it works. FWIW, the GV account is free - and the OBI box is about $50 at Amazon - and requires no subscription. It just taps into the GV SIP profile (completely automated, you don't need to have any computer literacy).
We shouldn't have to jump through all these hoops... But, quite honestly, if I didn't have this issue, I would never have found out about the OBi box. Now that I know how practical it is, even if wifi calling worked as advertised, I would still use OBi over the cell phone.
I can't say or add anything about a possible poor wifi radio on this particular phone, but we've had really good success with wifi calling and UMA on a 10/1 cable internet connection using wireless G, channel 11, WPA2, standard router settings (wireless QOS on, WMM powersave on- both phone are compliant, etc.) and SPI firewall turned off (NAT is sufficient for us). Our phones are Moto Defy and Samsung T339 and we've been using this service for 3.5 years with the Linksys T-Mobile router. Have you tried messing with the router settings?