In exactly two situations can you lawfully see who a person has been texting: the phone is yours, or it belongs to a minor you are responsible for. For another adult there is no reliable technical route at all — the honest options are their consent, a court order, or a licensed investigator, and every site promising otherwise is selling a credential-phishing page or a refund fight.
If you own the line. The carrier portal is the free first-party option and the one people forget: Verizon, AT&T and T-Mobile all show call and SMS metadata — numbers, dates, durations — for lines on your account, going back months. It shows who and when, never the words. On your own Android, Google Takeout exports your SMS archive in full.
If it is a child's phone. Screen Time on iOS shows who they contact, how often, and lets you set communication limits, but not message bodies. Google Family Link on Android manages the account without exposing content. That content gap is the honest reason a paid dashboard exists, and it only closes on a device you administer with the child aware of it.
Where Ultimate Phone Spy fits. The app runs on Android 4.0+, Windows and Mac, and pulls SMS, call logs and web history into one dashboard (sms tracker). It does not support iPhone, and it is not a remote install — Android requires hands-on setup on the device. Plans are $69.90/month, $40/month billed quarterly, or $16/month on the annual option (pricing).
The legal line, plainly. Reading another adult's messages without consent can violate the Wiretap Act and state two-party-consent laws in the US, the Computer Misuse Act 1990 in the UK, and GDPR in the EU — and evidence obtained that way is usually inadmissible anyway.
We covered the longer version in this thread.