VOIP, SIP, compatibility, 'real' Linksys SPA1001 how2ID, Polycom Soundpoint& more...

[unit_shifter]

Does anyone have suggestions for a primer, webguide, real life book, or overview of "what to shop for" if I want to set up a more serious home VOIP setup? (for SOHO use with non-garbage tier providers, ie real voip like callcentric/anveo)

For instance I was about to buy some "unlocked SIP phones previously used with Fonality" specifically a polycom soundpoint 550 recently... but realized I didn't know for 100% sure whether it would work with the services out there. Because I honestly don't know what i'm doing when it comes to assessing hardware. :-P

Some of the VOIP places have commentary on compatible hardware but they don't mention much beyond SIP phones, no info on how to program them for a new provider, i'll see comments on amazon talking about "polycom offers no support for reprogramming used phones for end users", I realize I dont know anything about provider locking or buying used hardware, how to find reviews or comments of who makes the best phones to use (this is low budget but might as well know whats garbage vs good so you can tell what a deal is) and similar.

Also if there's any additional info anyone has for how to find a couple 'real' Linksys SPA1001 adapter when searching online or craigslist. I know of this site voipfan.net/other/fakepap2.php or https://web.archive.org/web/20180227...r/fakepap2.php since the former doesnt load for me anymore - but that only covers the PAP2, not the SPA1001's. It's been suggested the SPA1001's were a highly reliable ATA adapter back in the day, however apparently there's more counterfeits and knockoffs than real ones and I was wondering if there is corroborating information for the above/additional info somewhere.