Storm Calling Problem

I have a Storm and recently it has had some changes when I call certain people.  When calling two of the people I call most frequently, it either rings once or goes straight to voicemail.  Both of these individuals have expressed to me that they never receive my calls and only get the notification that they have voicemails from me.  Neither of them have blocked my number, ignored my calls or had their cell phones off when I called.  Is there any solution to fixing this?