Let’s say you’ve done your calculations on your airtime down to the pennies. You’ve calculated transfer rates. You know how much you pay for airtime. So you think that sending an 15 kb email (with compression) over your Iridium 9555 will take two seconds and, therefore (at $1.44 a minute), cost you five cents.

So you would be surprised when you find out that that email would actually cost forty cents.

Where’s the airtime billing difference coming from? 

Minimum billing increments: gobbling up airtime behind your back.  

Minimum billing increments refer to how your satellite airtime use is calculated. Instead of simply counting up seconds and kilobytes by exactly how many you use (say, charging you for 32 seconds of voice airtime if you talk for 32 seconds) airtime is calculated in chunks of time, even if you don’t end up using all the airtime in the chunk you’re being charged for.

Every carrier has them, so unless you opt for a broadband unit like the Iridium Pilot, you’ll end up calculating them into your costs. Iridium, for example, has a 20 second minimum billing increment for voice or data. An average Iridium minute for a handheld unit like the 9555 or the 9575 is $1.44, so each billing increment is $0.48. 

Taking into consideration the minimum billing increments, a phone call over an Iridium handheld that lasts 20 seconds will cost $0.48, but a call that lasts 21 seconds will cost $0.96.

That’s an expensive extra second.

Inmarsat’s IsatPhone Pro has a 15 second increment for voice, with a minimum billing amount of 30 seconds. (And make sure you count in the full minute it takes to connect). 

Globalstar has a fairly reasonable data minimum billing increment of 15 seconds (great for email checks, especially since Globalstar generally has a very fast connection speed). Its minimum billing increment for voice is rough, though: a whole minute minimum and 30 seconds thereafter.

Even broadband units aren't immune. Inmarsat FleetBroadband, for example, has a 30 second minimum voice charge, and 15 second increments thereafter. For data, it has a 50 kb charge to connect, and a 50 kb charge to disconnect. After the FleetBroadband is on, data is charged in 10 kb increments.

The FleetBroadband data connection costs could be nearly completely mitigated by simply keeping the system on all the time (which is what the Iridium Pilot does). Many people don’t do that, however, because they’re afraid of running up their airtime bills if their laptop decides to update automatically (which is why we highly recommend Optimizer - it completely blocks all unwanted traffic over your satellite feed). 

Iridium Pilot Has No Minimum Billing Increment for Data 

One of the reasons we were so excited about the Iridium Pilot is that the Pilot doesn’t have a minimum billing increment for data. And while it still counts in the typical Iridium billing increments for voice, there aren’t the connection times to pay for (since the unit is always connected). There are no connection costs, no minimum billing increments for data - you just pay for what you use. It’s simple, clear, and fair. Check out our dedicated page on the Iridium Pilotfor more information.

Unless you go with the Pilot (or finagle your FleetBroadband), you’ll be dealing with billing increments, so it’s good to keep them in the back of your mind when comparing carriers and phones. Billing increments are rough on satellite airtime bills, and we feel your pain. Until the day they disappear completely (and we may be seeing the end, given Iridium's new data billing with the Pilot), we'll let you know which pitfalls to look for and how to get the best deals for your satellite airtime bill.