Are you talking about taking the internal antennas out of the gateway and mounting them outside? That's certainly possible, but IMO there are better options. It will be difficult to weather-proof and the adapters you need are less common.
I would buy four inexpensive single antennas that are rated for outdoor use instead. For example: https://www.amazon.com/Bingfu-Waterproof-T-Mobile-Cellular-Amplifier/dp/B07R9JGLV5/ref=mp_s_a_1_2_sspa
I’ll have to double check if they where ATT or not. I do not recall.
As far as how they work, you insert a micro-Sd card into the cell-link + 8 AA batteries. Then run the sdcard adapter down to the trail camera. Configure the trail cam, insert the sdcard adapter.
You use the SPYPOINT app to configure and view the pictures. Basically the camera sends the pictures to the micro-sd and the cell link transfers them.
I purchased these for use with them and had really awesome luck with extending cell signal -Bingfu 4G LTE Outdoor Wall Mount Waterproof Antenna SMA Male Antenna Compatible with Verizon AT&T T-Mobile Sprint 4G LTE Router Gateway Modem Cellular Trail Camera https://smile.amazon.com/dp/B07R9JGLV5/ref=cm_sw_r_cp_api_glt_fabc_Z6484Z55MBQPADZMSTN2?_encoding=UTF8&psc=1
Ran that to the top of the tree and went from like 50% signal to 90% - 100%