Only vodafone now. Basically the internet site they give you on most is a 1 year trial and they dont seem to want to take money to make it keep working, and being china based is horribly unreliable. When I was running one back when 2degrees had GPRS it was unreliable with reconnecting when moving between their own coverage and roaming to vodafone.

The call and get the location back by SMS seems fine on them, when they dont lock up from data issues.

There are newer ones that do LTE on them available, some others on here have had some sucess with them, but I am just perservering with the cheapies on vodafone, that is when the sim doesnt expire with no warning from the vodafone app so I have to do a dashboard disassmebaly to get a new simcard into the device.

Do all vodafone sims work, does the 4g sim step down to 2g/4g or do I have to find an old sim?

All work fine, just beware of the ones that snap apart to smaller ones if your tracker takes the big size. I ruined one because the sim started to seperate out when removing it and the edge tore off some contacts. So now I put some tape on the back of them to hold the middle micro sim in place.