Yes, on a Gigaset portable Dect phone connected to a Gigaset Base Station (as shown below) you can have up to 6 lines connected to the Base Station.
On a Gigaset Desk (as shown below) phone you can have up to 2 lines registered.
To find out how to add a new line onto your existing Gigaset phone please see below:
How to set up a new line on a Gigaset Dect phone registered to a Base Station - click here
How to set up a new line on a Gigaset Desk phone - click here