Bug 25146

In Bug #24906, when considering GSM feature-parity with ofono, I quoted ofono's own D-Bus API:

>       void Transfer()
>
>           Joins the currently Active (or Outgoing, depending
>           on network support) and Held calls together and
>           disconnects both calls. In effect transfering
>           one party to the other. This procedure requires
>           an Active and Held call and the Explicit Call Transfer
>           (ECT) supplementary service to be active.
>
>           This functionality is generally implemented by using
>           the +CHLD=4 AT command.

telepathy-spec contains an early version of Channel.Interface.Transfer, which has incompatible semantics, as follows:

Channel.Interface.Transfer
    requires Channel

    An interface for channels where you may request that one of the members
    connects to somewhere else instead.

    method Transfer (u: Member, u: Destination)

        Request that the given channel member instead connects to a different
        contact ID.

        Member (u, Contact_Handle): The handle of the member to transfer
        Destination (u, Contact_Handle): The handle of the destination contact

No rationale is given, and the text of this interface hasn't changed since the initial commit. I don't know whether there's a protocol that behaves like this; Rob, can you remember whether you had a protocol in mind when you wrote this?

The first step for this bug would be to do the multi-protocol research.

Triaging as enhancement/lowest since I'm not aware of any significant interest in supporting use of Empathy by receptionists and switchboard operators :-)