Summarize:

It's okay to try to compromise or persuade your parents if they say no. However, do not start complaining, raising your voice, or otherwise behaving in an argumentative fashion. This will only frustrate your parents and will greatly decrease the likelihood they'll change their minds. Avoid phrases like, "It's not fair!" This can come off as argumentative. Instead, try something like, "Okay, thank you for listening, but I feel like you're not hearing my side." If they say no, don't protest or plead with them. Show that you are mature by listening to what they say without reacting. Stay calm, and take a deep breath before you respond. Avoid arguments. Arguing with your parents won't change their minds; instead, they'll likely become more resistant to the idea of you getting a phone. Understand their response. If your parents say no, remember that they have a good reason. They have your best interest in mind, or may just not be able to add the expense of a phone right now. If money is a concern, offer to pay for some of the costs yourself. If you already have a job, say you'll save money from that. You can also offer to get a job to help pay for the phone. You can also offer to earn the phone in other ways. For example, ask if you can have a phone in exchange for bringing your math grade up. Say something like, "I could put $25 of my own money towards the bill each month." Whether you get a yes or a no, you need to ask your parents a few clarifying questions to know what you need to do next. If they say yes, ask them for their rules and expectations. Say, "I'm so excited about getting my new phone! How can I prove to you guys that you're making a good decision?" If they say no, ask them what you can do to show them that you're ready for a phone. Say, "What can I do to show you that I'm responsible enough for a phone?" If your parents say yes, then talk to them about when you can go phone shopping. If they say no, take steps to show your parents that you are responsible and reconsider how you can show them that you need a phone. If they say no, remember that you can ask again or they may reconsider, so try not to get upset. Instead, think about what you can do now to help yourself be successful the next time you ask. Remember, when you are asking your parents for the phone, never disturb them by again and again asking to buy the phone. They won't be satisfied with your behavior. If your parents seem hesitant, request a delayed response. Say something like, "I can see you guys aren't entirely sure about this. Why don't you take a few days to think about it and then we can discuss it again?" In the event that your parents are not at all willing to let you get a cellphone, politely accept this. If you accept a "No" with grace, this shows responsibility. Your parents may be more willing to change their minds down the road. End the conversation by saying something like, "Thank you for your time anyway. I appreciate you guys listening."
Refrain from arguing or complaining. Accept their answer. Offer to earn the phone. Ask for the details. Plan your next step. Request they think it over. Accept a "No" for now.