If you are an O2 Spain customer and you have even one trip planned for early 2026, O2 has quietly dropped a surprisingly useful “try it once” offer into the My O2 app: four days of free travel eSIM service via Telefónica’s eSimFesiLAG. The headline sounds festive, but the mechanics are very deliberate. This is O2 nudging everyday customers into a new roaming alternative, right when people start booking winter getaways and spring work trips.

Here’s what’s actually on the table, what you should watch for, and why this matters beyond four free days.

What O2 Spain is giving away

According to Telefónica industry coverage and O2’s own promo page, O2 Spain customers can claim four free days of eSimFLAG usage by accessing the promotion inside the My O2 app and completing the sign-up flow by 8 January 2026. Telecompaper+1

A key detail that makes this more than a “use it this week or lose it” gimmick: O2 says you have three months to use it. In practice, you can claim during the promo window, then activate when you actually travel over the following three months.

And yes, the “four days” are applied automatically as extra days in your purchase, so you are not hunting for a voucher code or doing a rebate dance.

How it works in real life

If you have used any travel eSIM before, the flow will feel familiar. You enter the My O2 app, tap the eSimFLAG promo, and you get redirected to eSimFLAG with your code already associated. Then you pick your destination and number of days, install the eSIM, and it will connect when you arrive.

eSimFLAG’s positioning is also very clear: it sells “unlimited data” travel connectivity, is fully digital and prepaid, and is designed so you keep your normal number while using the eSIM for data.

What you need to check before you get excited

• Your phone must support eSIM, which sounds obvious, but it is still the number one reason people abandon travel eSIM setups mid-checkout.
• eSimFLAG is positioned as data-only (no voice/SMS), similar to the “unlimited data travel eSIM” category you already know from brands like Holafly.
• “Unlimited” usually comes with network policy fine print somewhere. Telefónica and eSimFLAG market it as unlimited data, but always expect fair-use style constraints in the background, especially on very high consumption days.

Why Telefónica is pushing eSimFLAG through O2

eSimFLAG is not a random partner add-on. Telefónica has been building and scaling it as an international connectivity product available in around 170 destinations, and it has actively pursued distribution partnerships across the travel ecosystem.

This is the bigger story: telcos are increasingly treating travel connectivity like a standalone digital product, not just a roaming tariff. Instead of relying only on traditional roaming packs, they are borrowing the playbook from travel eSIM specialists: fast purchase, instant install, clear prepaid pricing, and distribution through apps, hotels, and travel partners.

Even the “four days free” move feels like the standard subscription funnel, applied to telecom. Give you a low-friction trial, let your next trip do the convincing, and then hope you top up later.

Market context: how this stacks up vs the usual travel eSIM suspects

If you have been following the travel eSIM category, eSimFLAG sits in the same lane as the “unlimited data, pay-per-day” crowd that became popular because it is simpler than gigabyte math.

Telefónica-friendly coverage is a selling point, and the brand has leaned hard into “one eSIM for all your trips” so you can keep topping up the same eSIM rather than reinstalling new ones every time.

Compare that to:

• Holafly-style offers: usually unlimited data packages per destination with a very consumer-friendly setup, but typically sold directly rather than bundled through your mobile operator.
• Airalo, Nomad, GigSky-style offers: more commonly fixed-data bundles where you pick X GB for Y days, which can be cheaper for light-to-medium users but less relaxing if you are working remotely or tethering a lot.

O2’s advantage here is not that it invented travel eSIMs. It is that it can put this offer exactly where customers already manage their mobile service: inside the operator app, with minimal friction.

Conclusion

O2 Spain’s four free days is not really a Christmas gift. It is a signal that big operators are done watching travel eSIM brands siphon off roaming spend, and they want a seat at that checkout screen. Telefónica has been laying the groundwork all year with eSimFLAG’s 170-destination footprint and travel-industry partnerships, and this O2 promo is a smart way to turn “I’ve heard of travel eSIMs” into “I used one and it worked.”

For travelers, the practical takeaway is simple: if you are already on O2 Spain, you can test a modern travel eSIM flow with almost no risk, then decide whether you prefer the operator-backed “pay per day, unlimited-style” approach or the classic fixed-GB bundles from specialist brands. For the market, the takeaway is bigger: travel connectivity is becoming a product category of its own, and telcos are starting to compete like digital travel companies, not like old-school roaming departments.