Thank you for contacting Geotab Support. Below are the answers to your questions.
1) We do not currently offer a wifi alternative on the GO devices unfortunately, but we do offer the use of the IOX IRIDIUM Satellite on the event that you lose cellular coverage, but at an extra cost and requires a supplemental satellite plan. It gives very limited information, and only updates every 30 minutes by default. You can find more information on it on the following webpage:
2) Currently, the US carriers are Verizon, Sprint, AT&T, T-Mobile, and Telefonica. In the case were the network you are using does not have coverage in the area the device is currently located in, we have "Partner Coverage", which means the device will automatically connect to the nearest cell tower and use roaming. You do not pay extra for roaming.
For a follow up, please create a support ticket through helpdesk, or contact your Geotab account manager so we can provide you with more information.
Have a wonderful day.