Test that the SIM card is fully functional
- Call any number (like your carrier’s free voicemail number)
- Press 2-SEND (ie the green call button); then
- Dial a new number (like your carrier’s free service line); then
- Press 2-SEND (ie the green call button); again.
- You should see two calls with one active and one on HOLD.
- Now press 3-SEND (ie the green call button);
- The calls should manually JOIN into a three way conference call.
- Then press some number keys and see if the tones are functioning
If this JOIN does not happen then you need to call up your mobile carrier’s customer service and ask them to “enable GSM Supplementary services for multi-party conference calls” This is known as Command [d] on the mobile network.
If your mobile carrier cannot provide you with this service on your SIM card, then you will need to change to a SIM card that can.