Typically, if you will use your home network SIM when you travel, your home network carrier must specifically enable the services you desire to use when you are traveling in order for roaming to function correctly.
If you intend to instead use a local SIM, then you first need to ensure that your BB is properly unlocked from your home carrier, and that also your home carrier properly releases your BB PIN from their BIS system when you use the local carriers SIM.
In any event, I recommend you ring up your home carrier for proper assistance with this.
Occam's Razor nearly always applies when troubleshooting technology issues!
If anyone has been helpful to you, please show your appreciation by clicking the button inside of their post. Please click here and read, along with the threads to which it links, for helpful information to guide you as you proceed. I always recommend that you treat your BlackBerry like any other computing device, including using a regular backup schedule...click here for an article with instructions.