On Cisco 6800 DECT MPP products (both DBS 210 and 110), if more than one line is provisioned on 6823 handsets and in case you receive a call on any line except the line 1 (which is the primary line on the handset) and wants to do supervised call transfer the 6823 handset does not display the "Line" softkey after you put the caller on hold to dial the party C and announce the call. Please note that this is not the case on 6825 handset model. On 6825 handset when you put the caller (Party A) on hold and select "New Call" softkey due to having multiple lines you need to select option "Enter Number" softkey and then select the "Line" softkey to be able to select the second appearance of the same line where you received the call on to make the outbound call to the Party C, with 6825 you will see the "Line" softkey but not on 6823 handset. Failure of not following these steps will cause the Base station to use the line 1 of the handset to initiate the call to the Party C and when uses the sip Refer message to request the Broadsoft AS to bridge the Party A to Party C uses the line 1 call info (Call-ID, From tag, TO tag) which AS doesn't have a dialogue on line 1 in it processing, so AS rejects the call. Therefore, the proper procedure is to have the end user to select the same line index where the Party A is on using the "Line" softkey, but because the 6823 handset model doesn't show the "Line" softkey the end user can't select the appropriate line.
I have opened a ticket with Cisco TAC (SR 697121822) and escalated the ticket to Cisco 6800 DECT development team, they came back that this is by design which is very odd that Cisco DECT product team accepted such a design where the above mentioned steps can be done on 6825 handset model and complete the supervised call transfer whereas the same action can't be done using 6823 handset model. In addition, Cisco does not make any mention about this such design in any of its DECT documentations. How Cisco expect the end users to do supervised call transfer using 6823 handset with multiple lines provisioned on their handset.
Later I found out by luck that if the middle button on 6823 handset gets selected on the above call scenario the multiple lines will get displayed on the handset and you can select the line where you received the call and you can do the supervised transfer action. So, it appears a cosmetic issue, but Cisco DECT development team has mentioned to me that such a design is because there is no space to display the "Line" softkey which it doesn't make sense because there are total of 3 buttons on the bottom of the 6823 display and each softkey can be displayed right above each button.
