Have you updated your PRL and Profile? Have you tried a SimPull? Any tower issues in your area? Also, there's an update just released this morning for the LTEVO, see if it helps with connectivity,
Settings > System Updates > HTC Software Updates
I'm having this problem as well, found this therad by searching 'tulsa'. Zip is 74135. Locations - I'm having dropped calls everywhere, but mostly on Harvard between 5th and 35th, and about a block east of 35th & Harvard. Seriously unusable - it's been going on for months but in the past few weeks it went from annoying to "don't even bother trying to call".
Thanks for the cross streets. I was able to use 35th and harvard and looked at the towers and the towers do not seem to reading anything out of the ordinary. Do you know if other Sprint users are having the same issues or is it just you? Have you tried to update your PRL on your phone?
Wife is having same issue - she's on the original EVO.
It's not the phone because I was having this issue, though not as bad, with my original EVO, then it actually got worse when I bought the new 4g lte EVO. I've hit up 'update prl' and profile etc.
Symptoms: I see one or even three bars of signal, then when I hit Call after the first ring it drops to 0 bars/no signal. Third or fourth time is usually the charm, and people I call have sort of gotten used to having 3 'hangup' calls in a row from my number. If doesn't get better soon I'm going to have to go with someone else.