BERLIN–Having repeatedly endorsed using prepaid SIM cards in unlocked phones when traveling overseas (most recently at NowU), I owe it to you to note when this normally-simple transaction goes sideways.

That was my story the first day and a half here. The afternoon I arrived, I went to the mall across the street from my hotel and discovered that the electronics store I’d used the last two years of covering IFA had closed. I went downstairs to a small Vodafone store and was told they were out of prepaid SIMs (no, really).

Then it was time for dinner, and by the time we got out all the stores were closed.

The next morning, I remembered I’d seen good reviews of some German wireless resellers at a crowdsourced wiki and another prepaid-data guide as well as on FlyerTalk. Meanwhile, a few of my dinner companions had suggested I check out two other telecom stores at the far end of the mall that I’d missed before.

The first had a decent deal but wanted cash when I only had €10 in my pocket–and the ATM, predictably located near the opposite end of the mall, refused to dispense cash for reasons I could not deduce from the German text. The T-Mobile store a few doors down, however, was happy to take plastic for a Congstar SIM with €9.99 credit.

First problem: After rebooting, the phone didn’t light up with the new signal, instead showing none at all. The shopkeeper pointed out that I had to set up the card online–which sent me back to the hotel to use its WiFi to configure the account. As Congstar’s site is entirely in German, I had to lean on Google to translate each page.

With my account set up and a data plan selected to use up that credit… I still had nothing. This was getting frustrating.

After a friendly but unproductive chat with Congstar’s Twitter account–they suggested trying the SIM in another phone, then referred me to a Web chat I couldn’t enter because the site couldn’t seem to deal with me posing an opening query in English–I gave up for the time being to attend Samsung’s “Unpacked” event.

Back at the hotel, a few other journalists sitting near me were fussing with phones. I asked if any of them had an unlocked phone with a micro-SIM slot. One did. He removed the SIM from his device, rebooted it and saw the phone immediately pick up a signal.

I put the SIM back in my phone, rebooted it, and finally had sweet, blessed mobile bandwidth. And I have absolutely no idea why that happened, or why it didn’t happen over the prior eight hours. Keep that in mind before you place too much trust in my tech advice.