Can I use my mobile phone when I travel? Can I use another SIM card abroad? The answer is yes if your mobile phone is unlocked and it supports the frequencies used in your destination.

What is a locked phone?
The lock is a software code that is put on the phone by the manufacturer. It is required by the carrier that sells the device, either because of the phone is discounted or having a contract. The lock ensures that the phone cannot be used on any other network.


How can I know my phone is locked or not?
Get an active SIM card from any local carrier different to the one you are using. Insert the SIM card in the phone and wait for the phone to load up. Try to make or receive a call on that SIM card, if the phone requests a network unlock code then it is locked. If you do not have another active SIM card or want to be sure, you can contact your carrier to check the phone.

Can I unlock my phone?
To unlock the phone, you need to enter a different software code. You can contact your carrier or look for a paid service from a third party.

What is "frequency band"?
Mobile phones communicate with the mobile networks by using radio frequencies. Sets of radio frequencies are called frequency bands. The frequency bands that a phone supports determine where and on which networks it can be used. Many modern phones support multi-band so they can run on different carriers and in different countries to facilitate roaming.

How can I check the frequency bands used by a carrier?
You can check the frequency bands used by a carrier by visiting its official website. If you have its contact, you can try to seek for help by call or email. There are different websites that list out the carriers worldwide, along with 3G and 4G bands and frequencies. Below are some examples:
Wiki: List of 3G UMTS networks
Wiki: List of 4G LTE networks
Frequency Check

Which bands does my phone support?
You can check the user manual of your mobile phone. If you do not have one, you can check the information on the official website of the brand. For example you can check your iPhone can run on where and which 4G LTE networks here: Apple iPhone on 4G LTE networks




How good is carrier coverage in my area?
The best mobile phone coverage is generally in urban areas, but have more physical interference. Rural areas have less physical interference but the signal coverage is often poorer. Even busy city centers have 'dead zones' where there is no network coverage. Signal 'dead zones' normally occur where signal between the mobile handset and the phone network cell antenna is blocked. It can be blocked by tunnels, hills or dense tall buildings.
Usually you can find the coverage map in the official website of the carrier. Check you location and see if it has signal coverage.