Open last month's usage report and sort the SIMs by data used. If your fleet runs on monthly per-SIM plans, look at the two ends of that list. At one end sit devices that finished the month with most of their allowance untouched. At the other sits a smaller group that ran past the limit and started paying overage by the megabyte.
You paid for both ends. On a monthly per-SIM plan, the data your quiet SIMs didn't use stays locked to those SIMs and expires on the last day of the month, while the overage on the busy SIMs lands on the invoice at a per-megabyte rate set outside the plan.
That is stranded data. It isn't a mistake by your team, because monthly per-SIM plans produce it by design.
A per-SIM plan assumes every device behaves like the average device. Real fleets don't. A parking sensor sends a few kilobytes a day, while a camera on the same site uploads a clip every time a car passes. A charger pulls a firmware update once a quarter and sits quiet the rest of the time. Put them on the same plan and you get waste on one side and overage on the other.
The standard fix is tiers, with heavy devices on a bigger plan and light ones on a smaller one. That holds until usage shifts, and sooner or later it does: a firmware update lands, a site gets busier, or a device starts retrying a failed connection every few seconds and burns its allowance in a week.
Someone has to notice, move SIMs between tiers, and do it again next month. On a fleet of a few thousand devices, that becomes a standing job nobody budgeted for.
Stranded data stays hidden because it sits in two separate places. The unused allowance is buried inside the flat plan fee, so nobody sees it, while the overage shows up as its own charge and gets all the attention.
Teams cut the overage by moving busy SIMs to a larger tier, which raises the plan fee on devices that will go quiet again next month. The total barely moves.
The three questions at the end of this piece test it against your own invoice.
A shared data pool removes the boundary between SIMs. You size one allowance for the fleet, based on average usage per SIM multiplied by the number of active SIMs. The camera draws on the headroom the parking sensor never touched. Per-SIM overage disappears because there is no per-SIM limit left to break.
IXT's Global Data Pool works this way across borders, so a device that changes country draws from the same pool. Pascal Technologies runs its vessel fleet on a 5GB shared pool. The boats cross between countries, and the cost stays predictable without overage on any single vessel.
Add up the allowance across every SIM. Did the fleet use less than that last month?
Did you still pay overage in the same month?
When one device starts using ten times its normal data, how long before someone on your team knows?
Two yeses mean you paid twice for the same capacity. Your answer to the third tells you whether you would catch a runaway device on a shared pool before it costs the whole fleet.
Want to see your fleet's usage as one pool? Book a walkthrough of the usage view in IXT CMP.
This article was first published on 20 October 2026 in Secure SIM Insights, IXT's weekly newsletter on LinkedIn. Subscribe on LinkedIn to get each edition when it comes out.
This guidance is based on real IoT and OT deployments in regulated industries including energy, utilities, and industrial environments.
IXT designs and operates secure connectivity architectures where:
The patterns described here reflect how these environments are secured in practice, not theoretical models.
This article was written by the IXT Connectivity and Security team.
IXT operates a full MVNO core network and delivers secure IoT connectivity across 190+ countries and 600+ mobile networks. The team works directly with industrial, utilities, and infrastructure operators to design and secure large-scale IoT and OT deployments.
Their focus is on network-level Zero Trust architecture, SIM-based identity, and secure device communication without relying on VPNs or endpoint agents.