Cordless phone breaks Wifi

[thinhnghiem]

Hi all,
I am facing an issue that needs some explanation
At my home, I subscribe a service including a telephone line and an ADSL, which share the same telephone number
The modem of ADSL line has both Cable and Wifi feature
For telephone, I have 2 phone machine connect in parallel with each other, one cordless and one normal machine
During the time I use laptop to connect to Internet through Wifi, if there is any coming call, and I pickup the cordless machine, Internet is disconnect
Everything is Ok when I pick up the normal machine
Could anyone of you explain to me why ?
Thanks
Thinh Nghiem from Vietnam