did you activate roaming on your Pay Monthly phones before you left?
For Pay As You Go mobiles, roaming is on by default.
Not so for Pay Monthly.
Log into your Virgin Mobile account then click on the "Plan and device" tab.
Go to "Manage my services" here you can set "Roaming" to ON & "International call barring" needs to be set to OFF.
If this was your problem, make the change by moving the "switch" in your account.(Click the other side of the rectangle box).
Too late now, I know but may be of help for next time.
If you want to say thanks > click 'Kudos'.Answered your question? > click 'Mark as Helpful Answer' also.