MCI trunks transmit either ANI only or DNIS only as 10 DTMF digits (no delimiters). The first three digits are the Numbering Plan Area number of the call; the remaining seven digits are the number of the calling telephone (see MCI ANI Delivery Protocol).
For example, the trunk will transmit ANI digits (such as 6135922122) or DNIS digits (such as 7035551212) in 10-digit format with no delimiters.