If I remember correctly, 99% sure anything sold from Cingular & Bell Atlantic came super locked down and you had to go through their SMS service to download the PRC files. You could enable developer mode by installing some app called HotSync, but then you had to find the software online to sync and those weren't easy to do.
I had a Treo from Cingular, it had absolutely no restrictions on installing programs. The preferred way to do so was generally by HotSyncing them from a desktop, but that wasn't any sort of developer mode, it was just how things were designed to work in the ecosystem (you wouldn't want to wait for the download over the air anyway).
There were a ton of aggregator sites for software with reviews, or you could just search the web for it, it was pretty easy.
All of Verizon’s phones were locked down with their BREW OS and proprietary VCAST App Store. Even doing something as simple as loading your own ringtones required heavy workarounds and sometimes third party software.
