I'm only speaking from my own very recent experience. When she was into me, everytime I called, she was there, or her friend was there to pick up the phone and tell me call later. When she lost interest, I couldn't reach her in more than two weeks on the phone. I say, try again tomorrow, if no one answers, leave a message and try again in the evening. If no one answers, forget it!!
Initially I gave this girl a lot of benefits of a doubt---not home, busy signals, going on the net perhaps, etc. etc. I thought I overanalyzed...I thought it was only my insecurities...but no, it was real--as a girl told me, when she wanted to get a phone call, she would always make sure that she was there to pick up a phone...So true.