Just so you know, I am a Stay At Home Dad and have been nothing else for 20 years. When Marissa Miller pulled the plug on working at home it was this sort of half halfheartedness that she was shaking out of Yahoo's business model. If your are working, then work and give either your employer or customers your complete attention. If you find yourself unable to separate from your child then stay home. You can't do both. Don't lie to yourself and your child that a cellphone is a replacement for your being there. It's not. When I married my wife we decided that childcare was of paramount importance. Since she was a well paid professional and I was a struggling student (Yes, I got that lucky), I stayed home. The son went to school in the day and I went at night, or he stayed with family. Yes, Family! You didn't disturb Mommy; Auntie, or Grandma, or Uncle or me or whoever took care of what needed doing. There was somebody who's job it was, and is, to take care of my son. As more children arrived my duties - Think about that word for a moment - Duty;
A 4 year old is not able to handle a phone and is too young to be allowed to make the judgement of when to call you. They need to know to call 911 in an emergency and stay on until help arrives - unless there is a fire, then they get out! Go to someone trusted and have then call for help. That is it. They should be cared for 24-7 and their caregiver will make any calls needed. If you can't trust your child's caregiver to make every fucking decision that needs to be made get another caregiver or do it yourself ! A cell phone will quickly become a stick to bully whomever is the caregiver. "If you don't give me more ice cream I'll call daddy and he'll be angry at you"
Save your money and send your kid to a good school. I always recommend a Montessori if at all possible. You will learn that one of the first steps to raising a healthy, happy and independent adult is having them learn to separate. They start to learn this at about 4. Yes you go away, and yes you come back. At school they learn to operate as a member of a society with rules and responsibilities. With family you learn to be part of a family. A mutually dependent social structure. That means every member needs every other. This is what you want, to raise a good person.