I will be using Asterisk, and we have a separate FXS/FXO gateway.
You will need a TDM400 FXO/FXS PCI/PCI Express card.
Can I register handset SPA302D without SPA232D ATA via SIP?
If you can configure the SPA302D with the authentication name, password and codec, then you can get away with direct registration to Asterisk.
Currently, I have an Asterisk/FreePBX on a Raspberry Pi. I have a 7960G, 7970G and an SPA122 (with two analogue phones) registering to my setup.