Hi David
From the data sheets for the 851W & 871W routers
=============================================
Management Features
? Cisco SDM
? Management of LAN switch ports
? Cisco Configuration Express
? Cisco Configuration Engine support
? DSL firmware update from Flash
? Cisco Service Assurance Agent (SAA)
? Telnet, Simple Network Management Protocol (SNMPv3), CLI, and HTTP management
? RADIUS and TACACS+
=============================================
As you can see CLI is available. The SDM web interface is designed for people with little or no experience of Cisco IOS but you can still telnet / console in and use the CLI if that is what you want.
HTH
Jon