I spent 10 days in the Philippines earlier this month and can give a few insights at how this works on the HTC One:
- Purchased the phone and renewed my contract late May. Had to wait 90 days for the unlock (inadvertently called Sprint Care 2 days before my 90th day to try to unlock the phone, International put my request through but the "approval" email did not come through until the 91st day activated)
- Went to UICC Unlock in Settings -> System Updates and updated my phone for unlocking
- Upon arriving in the Philippines, had to be setup with a prepaid micro-SIM
- Was able to get 2G and 3G coverage in the Philippines. As expected, did not get LTE in the country as their LTE bands weren't compatible with Sprint's version of the HTC One
So, in short, don't expect LTE usage internationally with the Sprint version of the HTC One, even using a local SIM, as Sprint's LTE frequency and band are really only found in the US.