NEC DSX 1093099 Feature Handbook page 167

Using Line-to-Line Transfer to set up a Tandem Call
To set up a Tandem Call via line-to-line Transfer:
1. Place or answer an outside call.
2. Press TRANSFER .
3. Place or answer another outside call.
4. Hang up to set up a Tandem Call between your initial call and new call.
DSX Feature Handbook
Tandem Calls / Unsupervised Conference
In these instructions:
[Super Display Soft Key]
[Keyset Soft Key]
Features ◆ 159