If I want to connect 2 PSTN lines in Australia to 3CX, and use 8 sip phones, with only 2 calls at once.
Can I use the Paton 4020 series? Other suggestions?
http://www.patton.com/products/pe_products.asp?category=315
No. The 4020 are for connecting FXS ports, i.e. standard telephones to a SIP server. You need FXO ports to connect your PSTN lines to a SIP server (3CX) . I use the Patton 4114 devices mostly but the 4112 (SN4112/JO/EUI ) would suit you with 2 FXO ports.