There are different types of cell phone unlock services. You can unlock your phone according to the service you need.  If your phone does not work with a sim card from another provider you need a network unlock service. Network Unlocking mobile phones is a common practice to allow the phone to work with other carriers. The unlocking process can be done by the phone manufacturer, an authorized service provider, or an independent third-party using a code.

If your Android phone has a passcode lock and you are not able to reset it since FRP is enable then you need the Google FRP unlock service.

if your phone cannot connect to a network or  is searching for a signal because it is blacklisted then you need the IMEI cleaning or blacklist removal service.

If you can't activate your iPhone because you do not know the Apple ID then you need iCloud unlocking service.

If you do not know the phone's history or you need to know the blacklist status or original carrier then you need IMEI check service.  

Network Unlocking your phone is the first step to getting started with a cell phone carrier.

Major carriers in the US and Canada such as AT&T, Sprint, T-Mobile, Rogers, Bell and Telus  offer their own unlock services.