Longer term, the issue is disparate frequencies. More than 40 different frequency bands are used by LTE providers globally. That means handsets need ability to use many different bands, a requirement that increases handset cost and carrier frequency planning.
But AT&T has become an early mover in LTE roaming, signing what many would say is the first-ever LTE roaming deal, with Rogers in Canada, in December 2013.
AT&T followed that agreement with a roaming deal with the U.K.’s EE, initially allowing AT&T LTE customers to roam on EE networks in the United Kingdom.
In February 2014, NTT Docomo and AT&T likewise signed a 4G roaming deal, allowing AT&T customers access to the NTT network when traveling in Japan.
Consider only the matter of differing frequencies used globally. In the United States, the 700 MHz, 850 MHz, 1.7 GHz 2.1 Ghz, 1.9 GHz and 2.5 GHz bands all are used for LTE service.
In Europe, the 800 MHz, 900 MHz, 1.8 GHz, 1.9 GHz, 2.1 GHz and 2.5 GHz bands are used.
In the Asia-Pacific region, LTE uses the 450 MHz, 700 MHz, 850 MHz, 900 MHz, 1.7 Ghz, 1.8 GHz, 1.9 GHz, 2.1 GHz, 2.3 GHz and 2.5 GHz bands.