Both SmartNode 4638 and Smartnode 4554 are using the same OS. Just both of them are have different number of BRI port. 4638 with WAN Port and 4554 without WAN port.
SmartNode 4638
* 3/5 Ports Quality ISDN VoIP - 3 or 5 ISDN BRI So ports, 4 or 8 low-bandwidth voice or T.38 fax calls. Advanced adaptive traffic management and shaping for maximum voice quality. Voice prioritization and DownStreamQoS
* Full Telephony Features - SessionRouter allows flexible call routing and numbering plan adaptations, CLIP/CLIR, hold, transfer, and much more.
* Management & Provisioning - Web-based management, SNMP, command line interface, & auto-provisioning for automated configuration & SW upgrades.
* Complete Access Routing - Two 10/100 Ethernet ports with auto MDI-X. Access router with NAT, Firewall, PPPoE, DHCP, DynDNS & VPN with IPSec*
* Full VoIP protocol support - SIPv2, H.323v4, MGCP/IUA, ISDN, DSS1, QSIG*, T.38, fax and modem bypass, DTMF relay.
* Outstanding Interoperability - Interoperable for voice and T.38 fax with leading SIP service providers and soft-switch vendors
SmartNode 4554
* Compact, reliable stand-alone gateway for VoIP systems—Connects an IP PBX or other VoIP systems to the ISDN PSTN, offering 2 BRI TE ports and 4 simultaneous voice or fax calls.
* Full SIP and T.38 support—Supports the complete range of industry standard VoIP: SIP, H.323, T.38 fax, fax and modem bypass, DTMF relay. Codecs G.729, G.723 etc.
* Transparent Telephony Features—Preserves ISDN features like caller ID and name (CLIP/CLIR), call transfer, hold, waiting, AOC. Supports DID and MSN lines in all major countries as well as complex numbering plan manipulations.
* Outstanding Interoperability—Interoperable for voice and T.38 fax with 3CX and other leading IP PBX systems.
