Roaming vs eSIM
T-Mobile is the honest exception in US roaming: Japan data is included on main plans. The catch is what happens after the high speed pool, per T-Mobile's own pages, checked late September 2026.
Experience More and Go5G Plus plans include up to 5GB of high speed data in Japan; Experience Beyond and Go5G Next include 15GB. After the pool: unlimited data at 256 kbps, per t-mobile.com.
Messages and a slow map tile work. Photos crawl, video calls fail, social feeds spin. For a weekend the included pool is genuinely enough; for two weeks of maps, translate and uploads, most people burn the 5GB in the first days and live on the crawl.
T-Mobile sells top-ups: $5 for one day and 512MB, $35 for 10 days and 5GB, $50 for 30 days and 15GB. Beside them, 10GB on KDDI for a week runs $12.44 and 20GB across 15 days $21.84, the live catalog checked October 22, 2026.
Light user on a short trip: keep T-Mobile, spend nothing, this page is not for you and we say so. Heavy user or longer trip: one eSIM keeps full speed for its whole data bucket while T-Mobile stays on for calls, texts and the included tail as backup. That combination is hard to beat.
Main plans include Japan roaming: 5GB or 15GB of high speed depending on plan, then unlimited at 256 kbps.
For messages and basic maps, barely. For photos, video and social, no. That tail is a backup, not a plan.
Short light trips, no. Longer or data-heavy trips, yes: full speed on KDDI for your whole data bucket while T-Mobile stays on as the calling line and backup.
Flying on after Japan?
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