SEPTA on Thursday unveiled electronic systems for the Internet and cellphones to give bus and trolley riders a clue as to when their next ride might show up.

However, the cellphone system won't work for T-Mobile or Sprint customers, about 25 percent of the local market.

The systems will give riders the scheduled time of the next four bus or trolley arrivals, but won't indicate whether the rides are on time. One feature will also show the last known location of the buses on any given route, so riders familiar with the route can estimate how soon a bus or trolley will arrive.

About 500,000 riders a day travel on SEPTA's 118 bus and eight trolley routes.

TransitView allows riders to see a map on the Internet (septa.org/transitview) from which they can select any bus or trolley route and see the GPS-reported locations of the vehicles on that route. Locations are updated every three minutes.

The cellphone application, SMS Schedules, allows riders to learn when the next four buses or trolleys are scheduled to arrive at a given stop. To use the feature, riders must know a new identification number for a bus or trolley stop. By texting "septa" and the stop identification number to 41411, riders can receive a text response with the next four scheduled arrivals for that stop.

Currently, the only way to find that stop ID number is on SEPTA's website, www.septa.org/stops. New signs will be installed soon at all 15,000 bus stops around the Philadelphia region that will include the identification numbers, SEPTA officials said Thursday.

The text system will not work for cellphone users whose service is provided by Sprint or T-Mobile. Those companies balked at providing the system free to users, supported by advertising with each text response, said Ron Hopkins, director of SEPTA's control center.

Another new program, Schedules to Go, expands offerings on SEPTA's mobile website (m.septa.org), enabling customers to get stop-specific information for the next 10 trips.

A similar system, TrainView, is already in use for SEPTA Regional Rail riders.

Contact staff writer Paul Nussbaum at 215-854-4587 or pnussbaum@phillynews.com.