Check your settings
If you want to answer an incoming call during an ongoing call, you need to turn on call waiting. Follow these easy instructions.
Find "Call Waiting"
Turn call waiting on or off
Return to the home screen
From the Call Waiting FAQs, worth a shot
If your Call Waiting isn't working, it may be because the feature isn't active on your line. To check:
If Call Waiting isn't listed, the feature isn't active on your line. Call *611 from your mobile phone and ask a Customer Service Representative to add Call Waiting to your line.
If it is listed, the feature is active on your line. Try turning your phone off and back on again. If you're still experiencing problems after doing this, call (800) 922-0204 from a phone other than the one that's having the issue. A Customer Service Representative will help you troubleshoot your issue over the phone.