Complex sentence: This creates additional inconvenience to the buyer as the phone cannot use a prepaid SIM from a different vendor while on vacation and as a result the subscriber must also sign up the often expensive roaming service offered by the vendor.
Split into simpler sentences: This creates additional inconvenience to the buyer, as the phone cannot use a prepaid SIM from a different vendor while on vacation. As a result, the subscriber must also sign up for the often expensive roaming service offered by the vendor.