Finally we can start making and flashing custom roms to the HTC Arrive.
We just need some Roms now. Hopefully we can get a few of the old Rom cookers back into the game. Ah a guy can hope right?
Anyway..
To get the HSPL (#3) go
Here
To Downgrade from the Mango Update's 4.3 Bootloader Go
Here
It is a pretty easy and straightforward job for the Sprint Arrive, I cannot comment on any other versions. And you must check that you have only 4.3 (or 4.X where X = any number) but the downgrade will not work without the Goldcard method if anyone has a SPL Bootloader of 5.0 or above. Just be warned. If you brick your phone, it is your own fault that you could not read these simple instructions and warnings.
Read, Read again, Be Patient, ???, Profit.