retailx,
I currently have 12 SPA1001 connected to 3CX just fine. I have 9 PSTN lines via 3 PSTN gateway devices.
You will need another device (FXO) to connect to PSTN line, such as a VoIOP gateway, besides the SPA1001. Here is a link to some recommended gateways.
http://www.3cx.com/support/voip-gateways.html
I am unfamiliar with VoIP providers, so I am no help there.
The SPA1001 was very easy to configure to work with 3CX.
Hope this helps.
Brian