WRT Verizon, I’m using two Spitz w/EP06-A on Verizon using a US Mobile SIM. US Mobile is a MVNO that offers Verizon as one of its options (the other being T-Mobile). The prices and flexibility are great IMHO, I only pay for data and it’s easy to add a GB mid-month.
Overall I don’t know what to recommend, however. The initial connection on a new SIM takes fiddling. I believe I had to first plop the SIM into a phone before the SPitz would get a registration, but it’s hard to tell whether that was necessary or whether just waiting longer would have done it.
The biggest problem is that I find the EP06-A firmware/driver immature. For example, uqmi ceases to work pretty rapidly. Sometimes it’s difficult to get a connection and I have the feeling it only works with qmi after the gl_monitor scripts have cycled through a ppp connection. I’ve also had situations where nothing worked and then I either rebooted or power cycled the device and bang! it just connected as if there had never been a problem. In those situations my suspicion is either the EP06-A firmware or a discrepancy between the linux qmi driver and the radio.