I have registered, I can make calls,,,but nobody can call me because I haven't got my number

I have had Magicjacks for Many Years now and I even us a free cell phone service call Freedom Pop. I you don't have the newest Magic jack please purchase it and then transfer your phone number to the new one. If you have the new Magicjack you can plug it directly into your router instead of in to the computer.
http://gethuman.com/phone-number/MagicJack/
Phone Number 561-594-9925
Talk to a Human
You get a recording, but do get to speak to an actual person. For billing matters only
Average Wait: 14 mins - Mon-Sat: 10am-7pm EST

http://gethuman.com/contact/MagicJack

Call customer support and make sure it is registered to the same device.

Go to http://www.magicjack.com/customercare.html. They can register your device, assign a phone number or port a number you already own.

Well, you'd best go to Magic Jack's web site, and either log in to your sister's account and cancel it, or try to find a Magic Jack customer support telephone number and make the call.

Hi,

I had a similar issue when changing suppliers in the UK. I had to get a PAC code from my old supplier to give to my new one so they could transfer my number over to them. I then discovered that my phone had been locked to my old supplier (the manufacturers auto lock some phones to the first network you use on the handset). Check your phone for a "network locked" message. I used an online unlock site which cost £7.90 and my phone was unlocked within 30mins. The old supplier took 9 days to send me an unlock code. I hope this helps.

I think there is a problem with the microphone. get a technician to dismantle the phone and replace the mic

Yes, most definately so. There are ways to boost the output signal of your machine but these days nobody has had to do it because lines are much clearer in the western hemisphere. The Magic Jack is great for voice calling but the faxes need instant responses from each other to progress through the initial training protocol and onto the document transmission. You may, if you have one, try another magic jack. It could be down to your particular Magic Jack. Try faxing without the Magic Jack.