So location matters. Virgin Mobile does not have towers but is a MVNO (see google if you want to know more?) and as such may not have any access to tower traffic data.

Sounds like tower congestion to me. More at https://www.google.com/search?hl=en&as_q=cellular+tower+congestion+all+circuits+are+busy&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=www.howardforums.com&as_occt=any&safe=images&tbs=&as_filetype=&as_rights=

Pretty well discussed and not easy for folk that want it to just work.
Bob