all of a sudden my texts are not being received, yet some are

[hsg130]

i text with my girlfriend all of the time.  starting monday, she can't receive texts from me.  i get them from her still.  i reply, but she doesn't receive them.  i send them directly using contacts and by entering her 10 digit number but to no avail.  now other friends of mine have confirmed they are not receiving my texts either.  i am using the newest apple iphone.  never had any problems until this monday.  ive tried everything recommended on this message board but nothing works.  seems like this is a fairly common problem.   i need a solution.