I've just about had it

[Saneta]

From: TOEIC listening part III, set 6, exercise 8:
— Oh no! I can't get a signal with my cell phone. I've just about had it with this cell company!
— Hmm, I can get a signal here. Why don't you try my cell provider? I've been very happy with them. I pay $60 a month, and they gave me a free phone.
— Only sixty dollars a month? My company charges $79, and I had to pay for my phone on top of that. Plus, you get better reception.
— Come on, let's go to my cell phone store. I'll introduce you to my sales agent, and she'll set you up.

What does it mean:
1.I can't get a signal with my cell phone.= I can't get/receive a signal from my cell phone/giving off from my cell phone?
2. I've just about had it with this cell company!= Just about like that I've had it with this cell company!?
3.I had to pay for my phone on top of that= I had to pay for my phone in advance?
4. she'll set you up = she'll deal with you?

Thanks a lot!!!

[Beeesneees]

- I cannot get reception on my phone.
- I'm fed up with this company
- I have to pay a monthly bill of $79 but I also had to pay the cost of purchasing the phone in addition to that.
- she'll sort you out a better offer.
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Cheers m' dears!