You cannot add "Grandstream GXP2160 HD IP Phone 6-line Colour Screen PoE Bluetooth: 6-lines and up to 6 SIP accounts. Dual Gigabit ports. Bluetooth. Rich 480x272 TFT LCD display. 5 programmable soft keys. HD audio on both handset and speakerphone. USB, PoE" to the cart because the product is out of stock.