I'm thinking to pick up a 1335, but I have a couple of questions before I do.
Looking at the available NIMs, it looks like they are all for T1/E1 connections. If I wanted to use a standard connection from an ISP modem, do I need an additional module, or will I simply be able to use one of the switch ports, in a separate VLAN, as the public interface?
That's exactly how you do it for an Ethernet-based WAN interface. You can have multiple security zones (policy classes) for public, DMZ, internal, voice, guest, etc. by VLAN. Each physical port can be assigned a zone/VLAN or be configured as an 802.1q trunk with multiple VLANs to another switch or an IP phone, etc.
Also, as in all Adtran devices, I'm sure it suppors L2L VPN connections. Does anybody know how many simultaneous connections it supports?
According to the datasheet at http://www.adtran.com/pub/Library/Data_Sheets/Default_Public/61700515E2-8_NV1335.pdf it supports 100 IPSec tunnels.