A Travel Query for the Hive Mind

OK, hive mind, I have a question for you. My sister is heading to London later this year, and this time she has a shiny new iPhone to take with her. She’s on T-Mobile, so allegedly she’ll have access to calling, texting, and low-speed data without doing anything. So here’s one plan:

• Download the maps she needs before she leaves.
• Rely on T-Mobile for calling and texting.
• Use WiFi whenever she’s at the hotel, in a coffee shop, etc.
• Register for The Cloud, and use that when she’s out and about.
• When all else fails, use T-Mobile’s low-speed data.

Alternatively:

• Buy a SIM when she gets there and use local calling, texting, and high-speed internet.

Do I have any T-Mobile readers who have been to London lately? What’s the dope? What do you think her best alternative is?

UPDATE: Thanks everyone! It sounds like T-Mobile’s native service works pretty well.