Yealink T28P handling multiple incoming calls

[macbeto]

Hi,

I have an Elastix 2.4 and I have installed Yealink T28P phones. When this phone answers a call and somebody makes a call to that phone instead ringing the Yealink the caller is send to the voicemail.
I would like to have multiple lines button in the Yealink and the ability to handle several calls at the same time.
Is that possible? how I have to setup Elastix or the Yealink phone for that purpose?

Many thanks. I am a bit lost in this issue.