The average small business wastes $1,200/year on phone lines it doesn’t need — and still gets busy signals during peak hours.
That’s because most businesses guess at how many phone lines small business operations require, then either overpay for unused capacity or underbuy and lose calls. There’s a better way to calculate this. And an even better way to eliminate the question entirely.
The Quick Formula (For Landlines)
If you’re on a traditional landline or PBX system, here’s the standard formula:
Phone lines needed = Peak concurrent calls × 1.5
Count the maximum number of people who are on the phone at the same time during your busiest hour. Multiply by 1.5 to add headroom. Round up.
Examples:
- If 3 people are on calls during your busiest hour → you need 5 lines
- If 6 people are on calls simultaneously at peak → you need 9 lines
- If 12 people are on calls at peak → you need 18 lines
Don’t know your peak concurrent calls? Here’s a rough guide based on business size:
| Business Size | Typical Peak Calls | Lines Needed | Monthly Cost (Landline) |
|---|---|---|---|
| 1-3 people | 1-2 | 2-3 | $60-180/mo |
| 4-10 people | 3-5 | 4-8 | $120-480/mo |
| 11-25 people | 5-12 | 8-18 | $240-1,080/mo |
| 26-50 people | 10-25 | 15-38 | $450-2,280/mo |
| 50+ people | 20+ | 30+ | $900+/mo |
At $30-60 per line per month, the cost adds up fast. A 25-person company might spend $500-1,000/month just on line rental — before long distance, features, or equipment.
Why VoIP Changes the Math Entirely
Here’s the thing: if you’re using VoIP instead of landlines, the concept of “phone lines” doesn’t really apply.
With traditional landlines, a “line” is a physical copper connection. Each line handles one call at a time. More lines = more simultaneous calls = more money.
With VoIP, calls travel over your internet connection. There’s no physical line to rent. Each user gets their own extension with effectively unlimited concurrent call capability. The only limit is your internet bandwidth — and each VoIP call uses about 100 Kbps. A basic 50 Mbps business internet connection can handle 500 simultaneous VoIP calls. You’ll never hit that ceiling.
The VoIP math:
| Business Size | VoIP Users | Monthly Cost (VestaCall) | Concurrent Calls |
|---|---|---|---|
| 1-3 people | 1-3 | $19-57/mo | Unlimited |
| 4-10 people | 4-10 | $76-190/mo | Unlimited |
| 11-25 people | 11-25 | $209-475/mo | Unlimited |
| 26-50 people | 26-50 | $494-950/mo | Unlimited |
No busy signals. No calculating peak concurrent calls. No paying for lines that sit idle 90% of the day.
VestaCall customers see an average 47% cost reduction when switching from legacy phone systems — based on data from 2,000+ migrations. A big chunk of those savings comes from eliminating per-line charges.
What About Dedicated Lines for Specific Uses?
With landlines, businesses often need dedicated lines for:
Fax line — $30-60/month for a line nobody uses more than twice a week. VoIP replaces this with virtual fax over email. No dedicated line, no fax machine.
Alarm system line — Some alarm systems require a POTS (plain old telephone service) line. This is one of the few cases where keeping one landline makes sense. But newer alarm systems work over cellular or IP, so check with your provider.
Credit card terminal — Old terminals needed a phone line to process transactions. Modern terminals use WiFi or cellular. If yours still needs a phone line, it’s time to upgrade the terminal ($50-100), not pay $30-60/month for a dedicated line.
Elevator phone — Building codes require emergency phones in elevators. These traditionally need a dedicated landline. Cellular-based elevator phones are now available and increasingly code-compliant.
For most businesses, the only equipment that might still need a traditional line is a legacy alarm system. Everything else has moved to IP or cellular.
The Real Question: Lines or Users?
If you’re asking “how many phone lines does my business need,” you’re thinking in landline terms. The better question is: how many people need to make and receive calls?
That’s your user count. And on VoIP, each user costs $19-35/month with everything included — call forwarding, voicemail, recording, auto-attendant, mobile app, and unlimited concurrent calls.
For a complete guide to choosing a VoIP system, including pricing comparisons across providers, we’ve got you covered. And if you’re comparing specific providers, our best VoIP for small business guide breaks down the top 8.
How to Calculate Bandwidth for VoIP
If you’re switching to VoIP and worried about whether your internet can handle it, here’s the math:
Per call: ~100 Kbps upload + 100 Kbps download
Formula: Max concurrent calls × 100 Kbps = bandwidth needed
| Concurrent Calls | Bandwidth Needed | Works On |
|---|---|---|
| 5 | 500 Kbps (0.5 Mbps) | Any broadband |
| 10 | 1 Mbps | Any broadband |
| 25 | 2.5 Mbps | Any broadband |
| 50 | 5 Mbps | Most business internet |
| 100 | 10 Mbps | Business fiber |
If your office has 25 Mbps upload speed — which is standard on most business internet plans — you can run 250 concurrent VoIP calls. You’ll run out of employees before you run out of bandwidth.
The more important factor is connection stability, not speed. Jitter above 30ms or packet loss above 1% degrades call quality regardless of bandwidth. For more on this, our VoIP call quality guide covers the technical details.
When You Actually Need More Lines (Even on VoIP)
VoIP solves the concurrent call problem. But there are cases where you need additional phone numbers (not lines):
Main business number — your primary inbound number. Every business needs at least one.
Department numbers — separate numbers for sales, support, billing. Useful when you want to track which department gets the most calls.
Local numbers for different markets — if you serve multiple cities, having local numbers in each increases answer rates by 4x versus toll-free or out-of-state numbers. VestaCall offers numbers in every US area code.
Toll-free number — for national businesses that want a professional, geography-neutral presence. Our toll-free vs local numbers comparison helps you decide.
Personal direct lines — for executives or key salespeople who want their own direct number.
On VoIP, adding a number costs $0-5/month — not $30-60 like a landline. So you can have as many numbers as you need without budget anxiety.
Making the Switch
If you’re currently on landlines and paying for 8+ lines, switching to VoIP is straightforward:
- Count your users — everyone who needs phone access
- Pick a VoIP provider — VestaCall starts at $19/user/month
- Port your numbers — keep your existing business numbers. VestaCall’s median porting time is 18 hours across 25,000+ completed ports
- Set up routing — auto-attendant, ring groups, call forwarding. Takes 30-60 minutes
- Cancel landlines — after porting completes
For SIP trunking — connecting existing PBX hardware to VoIP — that’s an option too if you want to keep desk phones but ditch per-line charges.
VestaCall setup takes a median of 12 minutes from account creation to first call — based on data from 10,000+ accounts. Start a 14-day free trial and test it alongside your existing lines.
How many phone lines does your business actually use right now — and how many are you paying for?
