How does the billing work on a pay as you go SIM for a GPSThe bill is a hefty one especially if you're traveling around Europe. To keep costs down you may want to look at a pre-paid monthly plan where you'll get a bundle of services (data, talk and text) for an affordable price.How much data will your device need per month? man down device This is a tricky question to answer as it depends on several factors including, your travel plans and how you're using the device.What you'll probably end up with is a choice between pay as you go and a pre-paid monthly plan where you can choose to pay in instalments or by the gigabyte.The best way to figure this out is to use a device that displays your data usage over time and lets you choose a top up method.This is also a great way to compare different data plans to find the one that fits your needs.