t in the smaller line sizes. Mitel, for instance, introduced a small, yet flexible analog PBX, the SX-200, that took a large market share in the under- 100-line market. And distribution strategies were evolving too. Manufacturers even bought some of their distributors. ROLM, for instance, had begun mostly selling through independent interconnect dealers with exclusive territorial fran- chises but ended up with largely internal distribution after buying up franchi- sees. This provided an exit strategy for some interconnect investors. The PBX acquisition decision largely hinged on renting versus buying. Dimension was not available for sale; it was rented, under state-by-state tariffs, by the Bell Operating Companies. In order to compete with the interconnect companies' advantage-that systems could be paid off and owned by their users, at little cost-the BOCs introduced new tariff schemes. One was called two-tier. It had a "Tier A," the so-called "fixed" portion, whose monthly price depended on the term of the contract and ended after the term's expiration, and a variable "Tier B," whose monthly price continued for as long as the subscriber kept the system. Two-tier was meant to mirror the separate leasing and maintenance costs of a PBX acquired under a capital lease. However, it was not a contract but rather a tariff, subject to the whims of state regulators; Bell only promised not to ask the state regulators to change the Tier A rates during routine rate cases. Later, after determining that many companies still trusted "the phone company" over a third party to install their PBX systems, Bell introduced a "Variable Term Payment Plan (VTPP), "[8] where the unitary monthly rate depended on the duration of the rental agreement. VTPP rates were the standard Bell PBX offer- ing until the 1983 detariffing of PBX equipment, which also led to the end of the analog Dimension series. The Integrated Voice and Data PBX Bubble Digital PBX systems came to market in the mid-1970s, but what benefits did they bring their end users,