About twelve years ago, I was contracted to integrate some new radio gear at the (now destroyed) Arecibo Radio Observatory. Granted, Arecibo was in an radio 'quiet zone' including cellular signals, so I stayed a couple nights in La Esperanza before traveling to the radio observatory. There were few working cell signals anywhere in this area, so I relied on sat phone to get calls in or out.
Even in downtown San Juan, cell coverage wasn't great, even when driving by several cell sites. Many of the cell monopole sites were overgrown with vegetation, while others were on sketchy structures atop buildings. In general, it was obvious the cellular infrastructure in Puerto Rico was installed and maintained on the cheap.