A smartphone (does not need to be active on a mobile network) or even an iPod Touch with a clock/alarm app could do those things.
I think that when it comes to reliability, a smartphone isn't a good fit for an alarm clock. I've seen the following problems with using smartphones as alarm clocks. These are all from personal experience, or the experience of a loved one:
- Lack of a big, physical, easy-to-hit button to snooze the alarm. Most of the smartphones I've seen require that you be able to focus your eyes on the touch screen and either touch the correct spot on the screen, or perform some kind of a particular swipe manuever. If you're in bed with someone else who's not familiar with it, and they're the first ones to grab the phone, they might be unable to snooze it, or they might do the wrong thing and shut down the alarm instead of snoozing it.
- Failure of the app to reliably function properly. My girlfriend swears by a particular Android app which has multiple levels of increasing alarm strength. She loves it very much. Then there was the day when she was a few hours late to work because it didn't go off. The phone was connected to power, and there was no indication on the phone screen that anything had gone wrong, but the alarm simply hadn't gone off. My guess is that, when the time came for the alarm to go off, the app crashed for some reason. When she re-ran the app, everything looked fine.
- Smartphones are just not loud enough. Once I nearly missed a plane because I was sleeping in a dorm in a second-floor room. It was at a sci-fi convention in Spokane, WA during the summer. We were the guests of honor at this con, and the con used a college campus for its events that year; the concom had put us up in an unoccupied dorm room. It was hot, and I was sleeping with the windows open, with my smartphone next to the bed. I awoke with the concom people pounding on the door; we had overslept by hours and it was time for them to take us to the airport. My phone alarm? It was going off full blast but I hadn't heard it. Why? During the night, with the window open, the road work crew had set up one of those big yellow generator-powered road signs. The sound of the running generator outside the window was enough to drown out the phone, and my sleeping brain had gotten used to the generator noise.
There's also the issue that some people really treat their alarm clocks badly (smacking them pretty hard to snooze them, for example), and I think smartphones are fairly fragile.