While I obviously can't guarantee anything (and I haven't done exhaustive testing with multiple SIMs in multiple locations, etc.), the process was quite smooth for me. I didn't have to do anything special other than the documented steps of setting APN information and the keepalive time. See, e.g.
The keepalive time apparently varies from carrier to carrier and may need to be as low as 30 seconds for some of them. I'm using 200 seconds with Freedompop. 300 seemed to be problematicm so I backed it down to 200.
And don't forget to cancel the trials of all the non-free services, or you'll end up paying for them.