A 3550 is a layer-3 device and so supports multiple IP interfaces; therefore you can access it (telnet, SNMP etc) on any of its IP interfaces, be they VLAN interfaces or Routed (physical) interfaces. On the 2900XL, 3500XL to change the management interface you shut down Interface VLAN1 and created a new VLAN interface (the Management VLAN).
Andy