That still leaves the U.S., which is high on any operator's list of countries for LTE roaming, but offering the service isn't so straightforward. That's because U.S. operators such as Verizon and AT&T Mobility use different parts of the 700MHz band, which offers superior coverage and is therefore the best alternative when roaming. The short-term answer is for the European and Asian operators to choose which U.S. operator to align with, Hadden and Ljunggren agreed.
"That is a choice an operator can make, but more importantly it is a choice that device manufacturers will make," Ljunggren said, and added that phones will still have roaming service using 3G.
In addition to 700MHz, devices that have implemented AWS spectrum (1700MHz and 2100MHz) will also be able to access LTE in the U.S. Where U.S. consumers will have roaming service, other than in Canada, remains to be seen. Verizon will introduce products when the time is right, according to Pica, who wasn't willing to elaborate about what bands its version of the Galaxy S4 will handle.
Enabling data roaming on LTE, which includes implementing signaling protocol Diameter, hasn't been easy, according to Martin Guilfoyle, vice president of new products and R&D at Syniverse Technologies.
Operators that want to offer LTE roaming can either connect directly with each other or turn to an intermediary like Syniverse and connect to multiple other operators via their platform. Guilfoyle has been working on this for close to three years, and last year really culminated in a trial and proof-of-concept that has now been turned into a production environment.
"It hasn't been a trivial task; it took a lot of planning," Guilfoyle said.
The current situation reminds him of when GSM was rolled out in the beginning of the '90s.
"There were pockets of roaming, and then all of a sudden everybody and their cousin wanted to have a roaming agreement with everybody," Guilfoyle said.
For operators, offering LTE roaming comes with both potential risks and rewards. That services have been slow to materialize has more to do with commercial considerations rather than network complexities, according to Mark Newman, chief research officer at Informa Telecoms & Media.
"Operators are concerned that if they don't get the retail pricing structure right, LTE roaming could end up cannibalizing their revenue from voice and SMS roaming," Newman said.
One threat is from users switching to services like Skype, WhatsApp and iMessage, which are already putting pressure on operator revenue, and will work even better on LTE with its superior performance.
"It is up to us to offer services that are so good users won't want to do that," Ljunggren said.