nowadays, many wildlife camera has cellular functions, most of them can only support 2G GSM network, a small part can support 3G WCDMA network. now 4G technology has been mature.
the speed of sending picture depends on network uploading speed. camera module needs to uploading images to network first, then email server or FTP server need to download them.
Below comparison is from thoery.
4G network uploading speed up to 50mbps
3G WCDMA network uploading speed up to 5.74mbps
2G GSM network uploading speed up to 2.7kmps
After testing, 4G=10times 3G=100 times 2G.