Narrowband IoT (NB-IoT) technology achieved a big milestone this week when two European operators, Deutsche Telekom (DT)  and Vodafone, completed an international roaming trial using global subscriber identity modules (SIMs).

The trial used NB-IoT modules and SIMs, which are modules that contain unique information tied to certain mobile network, from Deutsche Telekom roaming on Vodafone Spain’s network and SIMs and NB-IoT modules from Vodafone roaming on T-Mobile Austria’s network.

The GSMA, which oversaw the test, said that the trial demonstrated that operators can deliver a consistent level of service across networks. Plus, by testing certain use cases, like a smart meter deployment, the trial showed that features like incorporating a power-saving mode could be used even when NB-IoT modules are roaming.

The GSMA has a Mobile IoT initiative that has helped standardize and license cellular IoT technologies like NB-IoT and LTE-M in the 3GPP.

NB-IoT is a low-power wide area (LPWA) technology that uses licensed spectrum and can coexist alongside 3G and 4G cellular networks. It is different from LTE-M IoT technology, which uses an operator’s existing LTE network.

In Europe, DT has been pushing its NB-IoT reach. The company said in January that the technology was available in about 600 towns and cities in Germany, and that more than 200 companies are trialing the technology.

In the U.S., Verizon and AT&T have deployed nationwide LTE-M IoT networks, and Sprint has said it plans to deploy an LTE-M network. It is adding the technology to its tower sites at is makes its preparations for its 5G launch in 2019.

T-Mobile US, which is a DT subsidiary, has said it will have a NB-IoT network nationwide by mid-year. In addition, Verizon has said it will deploy a nationwide NB-IoT network across its footprint this year. The carrier recently completed a NB-IoT data session using Ericsson’s IoT software.