How to get text messages from another phone number?

Short answer: SMS is bound to a SIM and a carrier account, so you cannot pull another number's texts onto your phone unless you control that number or that account. Everything advertised as "enter a number, read their messages" is a scam, a spoof, or malware.

The three cases where this legitimately works.

1. It is your own number on a second device. Google Messages for web (messages.google.com/web) pairs by QR code and mirrors Android SMS/MMS into any browser; on iPhone, Messages on a Mac signed into the same Apple ID shows the same threads. Both need the physical phone once to pair, then stay in sync.
2. You are the carrier account owner. A SIM replacement at a carrier store moves the number to a new SIM and new texts land there. It is logged, it kills service on the old handset, and it is the honest way to recover a line from a lost or broken phone — or, with a death certificate, from a relative's line.
3. It is a minor's line on your plan. The child's Android phone with the family app installed, or carrier-level family controls that expose numbers and timestamps, both work because you administer the account.

What does not work, and what it costs. Number-spoofing "message readers" and SS7 interception services are fraud; using them lands you under the Wiretap Act (18 U.S.C. 2511) and the Computer Misuse Act in the UK, and they harvest your card details on the way. Sample-data demos are the most common version of this.

Where our app actually helps. Ultimate Phone Spy captures SMS and MMS threads, plus call logs and timestamps, on Android 4.0+ — and separately covers history on Windows and Mac. It goes on with the user's knowledge, on a device you administer: https://ultimatephonespy.com/sms-tracker. No iPhone support (iOS blocks device-level access), no remote install, and no "just the number" setup — if a vendor offers that, it is not doing what it says.

Free first-party options first: Google Messages for web for your own Android, iCloud message sync for your own Apple ID, Family Link or Screen Time for a child's phone. If another adult's messages matter in a legal dispute, the admissible path is consent or a court order, not an app.