Ok, did some traces on my PC, and mobile (HTC M9) on and off wifi calling and I can't say for sure that the routing to the IP address stays the same when on wifi calling BUT I can say, for sure, I'm not ending up in Arizona. I can also tell you, from having a buddy trace as well from a different state, he is not resolving to AZ or Colorado, where I actually am. Hope #8 has a big spike on my end and that is the first Sprint IP so I wonder if that is authentication point but everything else looks fine and not very much of a distance on my data route.
Here is my trace from my PC followed by traces from my device and a map of the trace. I don't know why you are having issues but maybe it's your ISP if you haven't tested from other locations? Regardless, I recommend you get a Wifi Connect router, it's free (as long as you stay with Sprint for 1yr) and if you use wifi calling, a lot, like I do, it is provided specifically to make that experience as good as possible (granted your ISP can hold up their end of the deal which shouldn't take much trying).
Tracing route to 68-31-54-1.pools.spcsdns.net [188.8.131.52]
over a maximum of 30 hops:
1 46 ms 2 ms 68 ms sprint.router [192.XXX.XX.X]
2 9 ms 44 ms 11 ms 10.100.128.1
3 58 ms 11 ms 48 ms 184.108.40.206
4 29 ms 80 ms 11 ms 220.127.116.11
5 86 ms 42 ms 43 ms dalsbprj01-ae1.0.rd.dl.cox.net [18.104.22.168]
6 25 ms 72 ms 25 ms ae-12.r08.dllstx09.us.bb.gin.ntt.net [22.214.171.124]
7 201 ms 27 ms 40 ms ae-5.r01.dllstx04.us.bb.gin.ntt.net [126.96.36.199]
8 29 ms 339 ms 26 ms 188.8.131.52
9 115 ms 32 ms 51 ms 184.108.40.206
10 49 ms 93 ms 50 ms sl-crs1-fw-0-4-0-2.sprintlink.net [220.127.116.11]
11 142 ms 50 ms 55 ms sl-sprin904-719781-0.sprintlink.net [18.104.22.168]
12 * * * Request timed out.
From my mobile:
for whatever reason the moderators didn't like my post, no idea why, nothing offensive, the only thing I can think of is I included a link showing your hop #11 is actually in or near Phoenix Arizona.
You happen to be wrong about your termination point, hop number 11, 22.214.171.124 is Arizona, you are taking a different route to get there but you are ending up in/near Phoenix, AZ (link was here pointing to a website that shows geographical information) Usually these sites are pretty accurate, at least within 10 to 20 miles.
Oh you have lousy RTTs starting at the first hop and then only gets worse from there. The problem is NOT my ISP nor anything along the way between my home and Sprint's Wi-Fi headend, problem is physics it takes 40 ms each way plus whatever time it takes to process the voice.
So until Sprint provides another termination point closer to me I'm going to have the problem regardless of what router I install.
I guess the latency issue doesn't matter much since the service is highly unstable on the Android platform, or at least on a 100% stock Galaxy S5. The service seems to work fine on the iPhones at the same location, then again they terminate the calls on a different host on Sprint's network.
Way to go Sprint in offering a stable service.