Some Philadelphia women now get doctor's-appointment reminders by text message.

Many of those message concern updating birth control administered by shot,  a popular contraception choice among young women who get their care at Spectrum Health Services center in North and West Philadelphia. The shot, sold under the brand name Depo-Provera, provides long-lasting pregnancy protection, but works best when a patient returns for a booster shot every three months.

Back in 2012, Spectrum clinic workers used to spend lots of time on the phone leaving voice-mail reminders.

"You actually have folks tell you, please don't call," said family doctor Ian Bennett. "For folks under age 30, text is the preferred form of communication."

Bennett and his team at the University of Pennsylvania are studying whether text-message reminders bring women back to the doctor at the right time.

At first, Spectrum's Chief Operating Officer Brenda Noel was skeptical.

But when she learned that about 90 percent of the health clinic's younger patients own a cell phone, she says she thought, "OK, maybe this can work."

"The cell phone is like part of them, it's always with them and they tend to respond much easier with the cell phone," Noel said.

Many digital-health applications require a smartphone or a desktop computer, but Bennett said the low-tech, text-messaging system was designed with low-income patients in mind.

"They're not sitting at desks all day reading email," Bennett said. "We really need to be working as a health system toward making our services more accommodating to that particular population."

The researchers are still gathering data on pregnancy and health rates, but they said the sign-up process was smooth.

Today more than 600 Spectrum patients have agreed to get their birth-control reminder via text-message.

Meanwhile, many studies are under way to test digital technology. Policy watchers and budget hawks say -- right now -- much of the research is focused on figuring out if the technology can be effectively integrated into the health system. There's still very limited evidence that mobile health interventions actually improve health.