The girl may call you to schedule a date, or you can call her to ask her out.
When you click the Phone command, there will be two options in Real Time Mode which are "Ask her out" and "Schedule a date." Only "Schedule a date" command is available in Skip Mode.
You use "Ask her Out" command when you play Real Time Mode and want to schedule a short meeting with your girlfriend. The locations are very limited and dependent on the time. For example, you only have some locations at school available on weekday morning and some restaurant or park available after school. The instruction on how to call your girlfriend and schedule a meeting can be read here. Note that when you ask a girl out, she will come to meet you immediately, so you don't have to select the time.
In the case that the girl calls you, you will hear ringing tone and see a pink phone icon at the Phone Command. Click Phone command to answer the phone. You girlfriend will pick the location (which will be shown with smiling heart icon on the map) and invite you for a date.
you usually have 3 choices when she calls.
1. Accept her date invitation. She will ask you to pick the time.
2. Reject her invitation.
3. Accept the date invitation but suggest another location. You will be able to pick your preferred location and pick the time.
In some cases, the girl may not be satisfied with either date or time, and will ask you to pick the new one(s).