I had a problem recently with a user who upgraded to XLite 5 SIP Softphone.
Regardless of the numbers and settings, XLite 5 will force you to dial in the international format, regardless of whether that is correct.
To get around this issue, dial x before any number which will make xlite think you are dialling an internal extension and therefore won’t play with the number dialled.
For example, x001555123456
More information: http://www.keshercommunications.com