Verizon Communications (NYSE:VZ), AT&T (NYSE:T), and T-Mobile (NASDAQ:TMUS) are constantly battling to keep customers. Most of their efforts are focused on individual and family subscribers that can switch between carriers with relative ease. But enterprise customers are also a massive revenue opportunity to carriers, and recent data shows that it's only getting bigger. 

The global mobile enterprise market will be worth $200 billion in 2020, according to ABI Research. And the research firm thinks U.S. carriers have the ability to tap large parts of this market.

"Operator services need to focus on driving the most value from the smartphone to the enterprise user, such as assisting in choosing the right devices and applications, and offering services to manage device content and functionality," ABI's managing director and vice president, Dan Shey, wrote recently. 

ABI also noted that offering "increasingly simplified, cost-effective access to voice and data services when travelling internationally" is important -- and T-Mobile knows this very well. 

Image source: T-Mobile.

The carrier launched its Mobile Without Borders feature last summer, giving postpaid, prepaid, and business customers unlimited calling, texting, and 4G LTE data in Mexico and Canada for no extra charge. This allows T-Mobile customers to use their current mobile plans in Mexico and Canada just as they normally would in the United States. Previously, additional charges and slowed data speeds would be triggered. 

T-Mobile had to make deals with other global cellular operators -- no small feat -- to pull this off. And the carrier's efforts leapfrogged AT&T's similar international expansion. AT&T then followed up a month later with its own free calling and texting to Mexico and Canada. 

In addition to Mexico and Canada, Verizon and AT&T have created partnerships with Tele2 and Vodafone to build out more services and solutions around the globe. That's a great move, but it's not the only enterprise opportunity open to the carriers.

Global Internet of Things
ABI mentions that more can be done to build the U.S. carriers' global enterprise footprint, particularly in the Internet of Things (IoT) category.

"Looking ahead, operators also need to help businesses leverage the smartphone and their voice and data connectivity services as a key component in their IoT solutions," ABI said. 

Image source: Verizon.

Nearly 5.5 million new things are connected to the Internet each day -- from shipping containers to wearable technology -- which opens up a massive cellular connectivity opportunity for U.S. carriers. 

Connectivity partnerships, where a carrier's enterprise solutions use another carrier's cellular signal, could help U.S. telecoms grab more IoT revenue. And it's coming at a good time: Verizon's 2015 IoT revenue was just $690 million, and AT&T's is likely to hit $1 billion (mainly from its connected cars) this year. To grow this segment, the carriers will need to look beyond U.S.connections to the broader global market. 

Looking ahead
North America is currently the largest enterprise market, but that's beginning to change. Enterprise mobile revenue in the Asia-Pacific region will surpass North America by next year.

If the carriers can't effectively build out global enterprise and IoT solutions, they'll end up forfeiting a $200 billion opportunity to other wireless carriers. U.S. carriers are expected to grow operating profits by just 2% over the next year -- mainly due to increasing pricing pressures from competition -- which means this global opportunity is something they can't afford to pass up.