For those of you who want to use your Sprint HTC One as a GSM phone and use it on another GSM network such as AT&T or outside the U.S., there is an easy way to unlock your SIM as outlined by XDA user Thatotherguy.
To do this, you will need a rooted Sprint HTC One.
Step 1. Download and install Terminal Emulator.
Step 2. Open Terminal Emulator and type:
am start com.redbend.vdmc/com.htc.omadm.test.TestMainActivity
Step 3. When you get a menu page, select “API”, then select “simlock” near the bottom.
Step 4. Reboot phone and test with a GSM SIM card.
Step 5. Dial *#*#4636#*#* on your dialer and choose “Phone Information” and switch to “GSM/WCDMA Auto”.
You may also have to set APN manually for the carrier you use, see here.
Here’s a YouTube tutorial on it:
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