Siemens History

History of ROLM, IBM, and Siemens Enterprise Communications

IntroductionSiemens Rolm history telizent support services

As a technical services company specializing in supporting Siemens PBX systems, we are often asked about the various models and branding of the products manufactured by what is now Siemens Enterprise Communications. This overview is the first in a series to provide an unofficial biography of ROLM, IBM, and Siemens with a focus on the associated product lines and set types which most frequently generate questions.

Historical Overview of ROLM & IBM

ROLM was an early innovator of private branch exchange systems (“PBX”) well before the 1984 round of AT&T divestiture.  Prior to 1984 most business users simply ordered service from AT&T which was analog (2500 sets) running off a central office switch.  ROLM Telecom was spawned from Rolm Mil-Spec Computers, with “Mil-Spec” referring to building customized and rugged (EMP-resistant) computers for the US military.  Leveraging the military computer controlled communications framework led to the concept of the computerized branch exchange or CBX which was carried forward in branding through the first half 1990’s.

ROLM quickly grabbed market share in the late 1970s and early 1980s when the focus was primarily on digital phone sets (“ETS” and later the “ROLMphone” brands were quite feature rich and popular with knowledge workers such as law firms and defense contractors).  ROLM had the second largest installed base based of hand sets, commonly referred to as “lines” in 1980.  Major product lines and timeframes were as follows:

  • CBX 7000 Family (known for its burned orange color and refrigerator-sized cabinet)
  • CBX 8000 Family (maintained the “ROLM orange” color and brand)
  • CBX 9000 Family (maintained the colorful heritage and added highly scalable multi-node capability of up to 20,000 stations spread across 15 independently survivable nodes designed around the requirements of NASA’s “Mission Control” facility in Houston,TX)
  • CBX 9751 Family (released in 1988 for larger line sizes)

IBM acquired ROLM in 1984 (same year as the AT&T Divestiture) not long after AT&T purchased NCR. At the time common wisdom was that telecom and computers were converging. These two technology giants chose to invest billions in the other’s traditional markets. Hindsight would later prove that neither investment into the other’s market space proved highly successful. The ROLM product continued to gain market share of installed lines as a result of IBM’s marketing, sales and manufacturing prowess.

The CBX 9751 product family has proven to be one of the most reliable and lowest cost of ownership options, especially when spread over 20-25 years. It had the most powerful bus design in the PBX industry allowing for non-blocking self capacity, a common limit of its competitors.  Additionally it has a distributed architecture with redundant fiber links and a high degree of redundancy.  This scalable and reliable architecture was a hit in large campus environments such as manufacturing complexes and higher educational institutions, and once in place, business cases to replace it have proven to be hard to make.
Due to power consumption and footprint very few of the ROLM Orange products remain in service, so it’s of little value to list the models and first generation of digital station equipment here.  However, inquiries about the CBX 9751 Models are common. Consistent with IBM tradition, the numeric models increment with capacity size as outlined below.

 IBM-ROLM Era CBX 9751 Models





Capacity Summary



Model 10



Cabinet stacks horizontally, similar to a lateral drawer cabinet but wider and taller at the three cabinet maximum.

From 100 to 600 stations, with 1 to 3 cabinets

Not Available


Model 20



Large refrigerator style cabinet not designed to be connected to a second cabinet.  Discontinued with the Model 10 release. Very few shipped.

Viable for 100 to 700 stations

Not Available


Model 40



Large refrigerator style cabinet designed to be connected to an adjacent cabinet.

Up to 2,000 stations in a 5 cabinet configuration

Not Available


Model 50



Same Cabinet Styles as Model 40

Up to 2,000 in a 5 cabinet configuration

Full Range of Redundancy Options


Model 70



Same Cabinet Styles as Model 40/50

Up to 20,000 stations. Multi-note capability via fiber Inter-node links

Full Range of Redundancy Options




ROLM’s PhoneMail voice mail platform was a major business communications innovation in the early to mid-1980s. Readers under 50 years of age may find it hard to appreciate the 1980s corporate culture of secretaries, “AAs” for the executives, and message pads assigned to groups of 5-10 workers.  Hence, the term “phone tag”, which consumed hours a day… especially in the days prior to email, instant messaging etc. The younger set need only watch a few episodes of “Mad Men” to gain a view into phone communications prior to voice mail, and other forms of non-simultaneous communications.

PhoneMail models were simply references to the ever improving miniaturization of computer technologies with packaging and capacities improving every few years.  The older “orange boxes” were the size of washing machines and consumed as much power.  Suffice it to know that PhoneMail lead the charge of voice mail. Many of the developers of ROLM’s PhoneMail were also key contributors to Octel and other messaging platforms which led to voice mail being adopted by the LECs and becoming ubiquitous by the mid- to late-1990s.

Station Equipment

A number of desktop products developed during the IBM-ROLM era helped to significantly enhance employee productivity.  These products were ahead of their time and would only later be eclipsed by PC-based applications becoming common plan in corporate environments.  One such product called the Cyprus Terminal included calendars and directories with automatic dialing. Many of the features later named “computer telephony integration” were present in these late 1980’s devices.  John Malone, then CEO of Telecommunications Inc, the largest cable operator at the time, would not give up his Cyprus until the late 1990s. (The migration away from Cyprus can be in part explained by a feature deficiency, a lack of backup and restore capability.)

ROLMphones were the mainstay desktop product family from about 1985 until 1993. The almond colored sets had a reputation for durability and had a no switch hook, which was a component otherwise subject to failure due to end-use abuse of “slamming the phone” down in anger. The ROLMphone used a magnetic switch solving this problem.  Model numbers and a brief description are as follows:

ROLMphone 120 – Single line set with 12 configurable buttons, no display

ROLMphone 240 – Multi-line set with 24 configurable buttons, no display

ROLMphone 240E – Multi-line set with 24 configurable buttons, with a display

ROLMphone 244 – Multi-line set with 24 configurable buttons and an RS-232 interface for accessing the data path on the same twisted pair line (“ROLMlink”, which was in essence a proprietary ISDN BRI concept) or running separate computer controlled (CTI/TAPI) applications.

ROLMphone 400 – Multi-line set with 40 configurable buttons and display, commonly used as secretarial stations with at least some of the buttons used as line-use indicators for a call coverage group.

ROLMlink technology may offer a glimpse into what motivated IBM to acquire ROLM in 1984. ROLMlink delivered two digital paths – voice and data – to every ROLMphone.  Prior to the shake out of LAN protocols, ROLMlink was a potential solution for unifying voice and data communication to the desktop.


During 1990 to 1993 IBM transitioned the ROLM telecom group to ownership of Siemens AG’s enterprise telecom business unit.  This group’s company trade name gradually morphed over the years from Siemens ROLM Communications, to Siemens Information and Communications Networks (Siemens ICN), and currently operates as Siemens Enterprise Communications.  Later articles will provide details on the transition of product names from the ROLM and IBM heritage to the Siemens product families.