I'm currently in New Zealand visiting from the US and using an iPhone 16 Pro. I've been roaming with T-Mobile, and even though I'm seeing 2-4 bars of 5G, the speed is super slow. Thinking it was throttling, I switched to a Sparks eSIM, which shows 3 bars of LTE, but honestly, it's barely any better. It takes forever to load things compared to back home. I know it's not a nationwide issue since I've seen other people with much better speeds. Any idea why this is happening? I've had similar problems during previous travels, too.
4 Answers
There could be a couple of reasons for this: 1) Your roaming plan could have a lower speed priority, or there might be a cap on data speeds. 2) It’s also possible your phone might miss specific RF bands, although iPhones are typically good for global compatibility.
It sounds like prioritization is a big factor here. Roaming with T-Mobile usually means you’re a lower priority compared to the customers who pay for local service. I had a similar experience in Japan—using a local WiFi hotspot was significantly faster than T-Mobile's service directly.
When roaming, your data routes back to your home network, which can cause major latency issues. That means slower speeds because your requests travel a longer distance. Even the travel eSIMs can be slow since they might connect back through hubs in HK or Singapore. If you really want faster speeds, look into getting a local eSIM from a NZ provider!
I've noticed that US 5G networks tend to be more reliable than what you find in other countries. It's common to hit a speed wall abroad, especially when roaming.
That’s so frustrating! I actually did a test on a local website, and it loaded super slow—like dial-up speed. Other folks around me were using their phones normally, so it’s definitely not the overall network.

I hear you, but I already bought an eSIM. I just did a speed test, and I’m getting 0.05 Mbps down and 0.14 Mbps up. What’s even going on with that?