D-Series & P-Series: A Decade
of Phone UX — From the First
Buttonless Desk Phone to
a Next-Generation Family
Digium · Sangoma Technologies · 2011–2021 · 2025
The phone family
A decade of desk phones, one design language
2012
D-series launches
D40, D50 and D70: the first phones designed for Asterisk and Switchvox.
2017
The D80
The touchscreen flagship with no physical buttons. Its first production run sold out.
2018
Sangoma acquires Digium
The D-series design language carries over.
2022
The P-series
P310 to P370. The P370 touchscreen flagship carries the D80’s interaction model forward.
2025
Back at Sangoma
Returned as a senior contract designer across phones, mobile apps and admin panels.
Role
Lead UX & Interface Designer, 2011–2021, then senior contract designer in 2025.
Scope
Every desk phone model, its firmware UI, and the iOS and Android apps, kept in sync across three GUI frameworks.
Approach
One design language, defined once in design tokens and an icon font, then fitted to each screen size and color depth.
Outcome
The language survived an acquisition and a hardware refresh with minimal changes, and became the foundation for the P-series.
Process · The Phone Lab
Delivering a consistent experience across the D-series and P-series families — each model with different screen sizes, color depths (8 to 24-bit), and GUI frameworks (FLTK on low-end models, Qt on mid-range, Android on the D80 and P-series flagships) — required building dedicated infrastructure. The company already maintained a competitor sample lab; I used that as a starting point and proposed building a parallel lab specifically for UI and UX design validation.
The lab grew to include all of our phone models, three popular competitor devices, our two headphone models, and sidecars for our top-tier phones — connected via a local network and PBX. This let us walk through the full onboarding experience on real hardware: language selection, phone registration, extension setup, calls, and transfers.
Two discoveries came directly from running phones continuously in realistic conditions. First, our low-end small-screen models didn’t render drop shadows and gradients cleanly — we simplified the UI for that tier, which actually improved clarity for all users on that device. Second, screens would flash briefly and unpredictably throughout the day. Engineers traced it to the phones updating every contact unnecessarily on each sync cycle, taxing the OS. Without the lab, this would have shipped as a customer complaint.
To simulate scale — large call volumes and company-wide conference calls that a physical rack couldn’t reproduce — we repurposed a load-testing utility built by our senior engineer, adapting it to simulate over 100 concurrent calls.
Each model presented unique challenges. Different sized displays from different manufacturers, multiple BLF key configurations, and a buttonless touch only model.
Process · Cross-Framework Design Consistency
Each phone model ran a different underlying GUI framework — FLTK, QT, and Android — with our mobile apps on iOS and Android as well. A design decision that worked in one framework required a completely different implementation in another. To maintain consistency, I proposed and helped establish a tokenized color system, defining values once and mapping them to each environment's implementation via a separate specification document. It gave engineers a single source of truth regardless of which framework they were working in.
On our smaller, budget-conscious models, screen real estate and processing power were both limited. After reading about icon fonts, I proposed replacing our custom icon set with an icon font system. Engineering implemented it, and the change delivered three benefits at once: reduced storage footprint, improved system responsiveness — making the UI feel noticeably snappier — and eliminated localization ambiguity that had crept into some of our illustrated icons. One idea that solved a design problem, a performance problem, and an internationalization problem simultaneously.
Each model presented unique challenges. Different sized displays from different manufacturers, multiple BLF key configurations, and a buttonless touch only model.
The P-series · The family continues
When Sangoma acquired Digium, the D-series UI design language I had established became the foundation for the next-generation P-series — updated hardware running on Android, with physical volume and navigation keys added alongside the touchscreen for users who preferred tactile controls. The P370, the executive flagship at 7″ 1280×800 IPS with built-in Bluetooth and WiFi, carried the same interaction model forward. The same application suite, the same visual system, refined for newer hardware. The design was coherent enough to survive a company acquisition and a hardware refresh with minimal changes — which is its own measure of success.
What customers and installers said
On setup
“The self provisioning feature makes phone deployment very quick and easy.”
Enterprise IT customer, 100+ locations
On setup · P370
“Setup was quick and painless…”
Installer provisioning a P370, 2022
Start with the flagship
How do you design a buttonless phone?
The D80 had to do everything the D70 did, without the keys. Start with the person who has never used a touchscreen, and make sure they never miss the buttons.
Read the D80 case study →