This list shows these countries where it's impossible to buy a local prepaid SIM card (for data) at the moment. This can be because of lack of technical infrastructure or legal reasons which prohibits the purchase of a SIM card for foreigners. As you see, this list is rather short:
In Cuba there are still no data on their GSM network, not even GPRS on the only state-owned mobile provider "Cubacel". The only way to log on the internet for foreigners is to go to one of the major hotels or public WiFi hotspots. The situation is about to change with the easing of the US embargo. First 3G cells are now operating in Havanna and Varadero, but for roaming customers only.
Eritrea was the last country in the world to adopt a mobile phone system. It's sole provider Eritel is hardly accessible to foreigners as it requires a resident's permit, a very high connection fee and some weeks to get connected to a network mostly 2G-only with few 3G cells. There is a separate CDMA network covering 85% which is not compatible with most GSM phones.
The state-owned provider "koryolink" sells SIM cards to foreign visitors for their 3G network on 2100 MHz: a "Visitor Line" with 3 different packages on prepaid and a postpaid "Foreigner Line" for residents. Unfortunately, the Visitor Line has voice and text only, but no data. This can only be booked on the Foreigner Line at astronomical rates, but is inaccessible to short-time visitors.
The only provider Telecom Niue has a 2G/GSM network, but not for data, only voice and SMS. Visitors can have internet connection through Niue's extensive WiFi network with hotspots all over the island after paying NZ$ 25 for 5 GB in 14 days (for more info check here).
The two mobile providers SPM Télécom and Globatel only offer 2G without any data in this French Overseas Department. This leaves this area as only territory without own 3G coverage in America, but ADSL internet access and a widespread public WiFi network are available.
Transnistria is the only populated region in Europe without a 2G or 3G GSM coverage as the only provider "IDC" uses CDMA and EVDO only which is incompatible with GSM-devices. This situation may change as a 4G/LTE network on 800 MHz is being built, but not yet open for prepaid.
Lord Howe Island (Australia) Edit
On Lord Howe there is no mobile coverage. There are paid WiFi hotspots at visitor information center, museum and few other places but the rates are not published. Some hotels provide complimentary WiFi. Connection is slow as it goes through a narrow satellite link.
Pitcairn Island (UK) Edit
There's no mobile coverage on Pitcairn island. There is a fixed internet service provided in some accommodations, sometimes with a WiFi router, so you can connect through WiFi to it. All data goes through Inmarsat, so latency is high, speed is low and traffic is expensive. There is a tiered tarification to discourage large downloads. The exact prices are not published online. Outages lasting weeks are not unheard of.
Tristan da Cunha (UK) Edit
There is no mobile coverage on Tristan da Cunha. Since 2006 there is an internet café with a VSAT. 1 Mbps shared by all users, so it will be slow. Internet cafe has a place to use own laptop but it's unknown whether it's Ethernet or WiFi. Price for visitors is GBP 10 for the duration of the stay but it's not published online so this number is likely outdated.
South Georgia and the South Sandwich Islands (UK) Edit
There is no publicly available telecom services on those islands. You'll have to rely either on your ship's services or your own satellite link. If you're employed there, you will need to contact your employer for info that applies to you.
The only provider Norfolk Telecom has a 2G/GSM network, but not for data, only voice and SMS. Visitors can have internet connection through some WiFi hotspots on the island.
Christmas Island (Australia) Edit
After CiiA shutdown the only provider on this island is Telstra on 2G without any data connectivity. Speedcast has picked up their 4G network but the situation is still volatile as they have only a temporary contract to provide this network until June 30, 2017. It's unknown whether they sell new sim cards or just provide network to old customers.
There's only one network (IOTT) there on 2G for calls and texts, no data connectivity. Furthermore for a population of 600 IOTT has a backhaul of 2 Mbps, that's total, not per person. Fortunately there's an NBN installation going on, so you might be able to connect through them via WiFi in near future, possibly already.
Their only operator (MINTA) is working on installing 4G some time in the future. Meanwhile their network is 2G-only without data. You can use their hotspots as an alternative.
Turkmenistan is a very restricted Asian country where they sell SIM cards with data, but for visitors it proved to be impossible so far to get one. The only ways are illegal or for long-term residents with special status.
Uninhabited territories Edit
Obviously there is no mobile coverage or WiFi hotspots in uninhabited territories. As there are too many of them, it's impossible to enumerate, hence they are grouped in this entry. Your only way to connect would be to bring your own satellite link installation.
Greylist EditThis list shows these countries, where you should think twice of buying a local prepaid SIM card, as it may not be advisable under all circumstances. Because of certain procedures, legal barriers or technical restraints, you may be better off looking for alternatives like WiFi hotspots or an international roaming SIM. But check articles first to see what's restricted and if it applies to you and your purposes.
To buy a SIM card in Algeria, you need to present a certified copy of your passport to the provider. This needs to be made at a local mairie (town hall) at office hours before you walk into any operator store.
It's easy to buy a local SIM card from one of the providers as a new centralized registration system for foreigners has been implemented. The country remains greylisted as an additional IMEI registration system is in place for all devices using a local SIM.
Because of the "Great Firewall of China" a.k.a. censorship your internet can be severely restricted. Facebook, Twitter, Google sites like Maps, Gmail or its search engine and many others are blocked. Furthermore, China is starting to clamp down on VPNs used to circumvent these blocks.
Diego Garcia (UK) Edit
This remote island in the Indian Ocean is served by Sure on 2G only, but there is landline DSL at low speeds too. Lacking a submarine fiber link, prices remain high and speeds low for C-Band satellite connections.
Equatorial Guinea Edit
Foreigners can buy a prepaid SIM card not in usual operator's stores, but only in two special branches of GETESA (Orange) in Malabo and Bata.
The sole operator Sure on the islands has 2G only up to EDGE speed without 3G or 4G, but almost everyone in Stanley has ADSL internet service instead.
India has a very unforeseeable policy of registration which can take a few minutes, but also more than a week. So you'll never know, when you will actually be connected to the network after having purchased a new SIM card.
Japan is one of the few countries with no 2G/GSM network and much of its 3G is on very own frequencies. Furthermore, it bans the purchase of voice SIM cards to travelers by law. You can still buy data SIMs or rent a device or SIM card at many rental agencies.
The Palestine Territories have their own networks, but are restricted to 2G and data up to EDGE speed only. This is due to the refusal of Israel to grant 3G spectrum to Palestine operators. You may use Israeli providers instead.
Turkey has implemented a scheme of paying a TL115 tax for all imported devices to be used with a local SIM card. This is added by a whitelist registration system of IMEI numbers. If you don't follow the rules, your device will be blocked after a few months. So it only bothers you, if you want to stay longer or keep your SIM for another visit.
The only mobile operator of this island nation Tuvalu Telecom offers slow 3G only emitted over one antenna. For the capital better buy WiFi vouchers for data, outside only satellite phones will work.
Ukraine - Donesk and Lugansk regions (see Ukraine article): Edit
Due to the ongoing conflict in the Eastern part of the country, no 3G networks could have been deployed there yet. Mobile internet is only through 2G networks at EDGE speed (max. 150 kbps).