I'm using the Ardusimple Wifi NTRIP Master that I tether to an iPad and it works perfectly.  I've tried the 4G Master as well.  It connects to my base and acts like it is working just fine but I don't maintain a stable RTK fix.  The board requires a TMobile or ATT sim card and I'm in a strong verizon area.  The SIM cards I tried were on the Tmobile network but were subsellers.  I think that was the issue.