Ques. I have a Airtel broadband connection and a dlink 2750u router with modem. i connect rj11 to my modem plus router directly . but now i am thinking of getting a Wimax Connection. Isp told me that they will provide rj45 only. so can i connect rj45 to my dlink 2750u to create wifi or will i have to buy a new router only?
What you are currently having is a ADSL 2+ Modem/Router. If you connect the ISP provided RJ45 to the Router it won't make a difference as you would be connecting your WAN link on your LAN port.
So, yes you will have to buy a new router. That has a Rj45 WAN port in place of rj11.
We would suggest you to go with TP-LINK TL-WR841N 300Mbps Wireless N Router
It comes with two 5 dBi antennas for enhanced Wi-Fi coverage and signal strength.
Which is more than your current router.