I have given up on Network Manager after months of trying to get it to work right, this both in the Mint 17 series (based on Ubuntu Trusty) and Mint 18 (based on Ubuntu Xenial). It has more bugs than a garbage dump full of cockroaches that aren't getting fixed. I get by using WICD which occasionally disconnects but is relatively easy to reconnect. The problem is that WICD doesn't support USB 3G connections which I sometimes have need of. I tried Sakis3G but couldn't get it to work, perhaps because configuring it is above my pay grade. Is there any other simple plug-and-play alternative for using a USB 3G dongle that will work with Mint 18 with Mate desktop?

I've used a number of 4G and LTE and phones on Debian and Ubuntu that seem to work fine. (only one wimax) However there are millions of reasons you may be having issues.

Try some of these ideas maybe.

https://askubuntu.com/questions/9408...h-command-line
https://wiki.debian.org/Modem/3G

I am not sure using a command line will help but it is worth a try for sure.

Thank! I'll give wvdial a try. Network Manager doesn't stay connected for long enough to be of any use, and then it takes some coaxing to get it to reconnect,