Complex sentence: For those returning from the trail, be warned that the last bus is around 7:30PM and mobile phones are unlikely to work here (one is more likely to get a roaming signal from the mainland than a Hong Kong signal).
Split into simpler sentences: For those returning from the trail, be warned that the last bus departs around 7:30PM. Also, mobile phones are unlikely to work here (one is more likely to get a roaming signal from the mainland than a Hong Kong signal).