A watermark is inserted or overwritten into a packetized voice stream in a VoIP environment to characterize the voice data stream for various functions, such as providing certain in-band audible information or markers for detection. A visual type of marker can be inserted to measure delay for various applications, such as the round trip delay associated with providing directory assistance services, including measuring the delay from providing a prompt to a caller to the their response. The visual marker facilitates use of processes to detect measuring points for measuring delays. Audible markers can be used to provide various types of audible signals, including informational tones to agents, as well as announcements to callers.