voip supply has them listed as the same part.
http://www.voipsupply.com/aastra-536m
i have a 57i phone that I ordered this for - and decided to buy a 560 instead.
this is the product description:
The Aastra 536M expansion module is designed to increase the power and flexibility of the 5i Series SIP telephones. Up to three modules can be used with the 55i, 57i or 57i CT telephone to create a powerful, feature rich console option.
- Supported on the Aastra 55i, 57i or 57i-CT Phone
- Daisy-Chain up to 3 Expansion Consoles
- Add up to 108 Additional Line Keys
Aastra 536M (M670i)
The
Aastra 536M shares power and signaling with the phone, eliminating the need for additional wiring. Designed for receptionists, administrative assistants, call center agents, power users, and executives who need to monitor and manage a large volume of calls on a regular basis, the 5i Series Expansion Modules provide an intelligent choice for all Enterprise IP environments.
Aastra 536M Expansion Module Overview
Flexible Features The 536M is equipped with LED status indicators and supports a variety of programmable features including Line, Speed Dial, Busy Lamp Field, Bridged Line Appearance, Shared Call Appearance and Do Not Disturb.
Simplified Deployment Sharing both power and signaling with the 5i Series phone, the 536M can be easily added without additional installation or wiring expense. Simplified configuration via WebUI or configuration file from the phone.
Expandability Up to three 536M modules can be used with the 5i Series models 55i, 57i or 57i CT, offering up to 108 additional keys. Growing businesses can start with a single module and add more as their needs increase.
Aastra 536M Features and Functions
- Supported on the Aastra 55i, 57i or 57i-CT Phone
- Daisy-Chain up to 3 Expansion Consoles
- Add up to 108 Additional Line Keys