Two cases:
1. I put a call on hold myself. As Tony writes in comment #2, the dialer UI toggles the button icon and gives haptic feedback. I don't think any additional sounds are necessary here.
2. The far end puts my call on hold. The operator may play a "you are on hold" audio message, or it may send a "supplementary service related network initiated notification" (see 3GPP TS 27.007 "AT command set for User Equipment", section 7.17 "Supplementary service notification"), or neither.
The lower layers of our telephony stack already listen to those notifications (signal RIL_UNSOL_SUPP_SVC_NOTIFICATION in the RIL API, property org.ofono.VoiceCall.RemoteHeld in the oFono API), but we should indicate this also to the user (visually/haptically/audibly). There is also a very similar case "your call has been added to a conference call".
At least in my initial tests in Sonera/Finland network, these notifications are not received. I'll have a closer look.
Two cases:
1. I put a call on hold myself. As Tony writes in comment #2, the dialer UI toggles the button icon and gives haptic feedback. I don't think any additional sounds are necessary here.
2. The far end puts my call on hold. The operator may play a "you are on hold" audio message, or it may send a "supplementary service related network initiated notification" (see 3GPP TS 27.007 "AT command set for User Equipment", section 7.17 "Supplementary service notification"), or neither.
The lower layers of our telephony stack already listen to those notifications (signal RIL_UNSOL_ SUPP_SVC_ NOTIFICATION in the RIL API, property org.ofono. VoiceCall. RemoteHeld in the oFono API), but we should indicate this also to the user (visually/ haptically/ audibly) . There is also a very similar case "your call has been added to a conference call".
At least in my initial tests in Sonera/Finland network, these notifications are not received. I'll have a closer look.