Sometimes can't receive calls

I am hoping somebody can help me with my problem. I searched through the forum(s) and found nothing of what's happening to me.

My Problem: Ever since I started Alltel (January?) I've had points in time where I can't receive calls or text messages. It isn't constant and it isn't limited to one number. People sometimes call or text me and I don't get their voice mail or text until later on in the day and sometimes even later in the week. This sometimes last me for a whole day to where I don't know anyone's calling. Their number doesn't even show up in the missed call list so I know it isn't getting all the way through.

What I have done to try and solve it: First I tested it. I used my brothers phone (also from alltel) and called my number and it worked. Later on I tried my number again and it didn't work.

My friend sent me a text message once and I looked at when he sent it and when I got it and it was 4 hours apart.

It isn't my location that is messing with it because my mom and brother both get great reception. I called Alltel support and they had me do a bunch of steps (*228, etc.) and still there was no difference. They then suggested getting a new phone. So of course I listened (phone = samsung snap). Still even with the new phone I get the same problem.

If somebody could help it would be greatly appreciated. Thanks.

What type of phone are we talking about here? Was the number the phone uses ported from another provider?