The IT Director's 90-Day Plan for Replacing a Legacy Phone System

You just became the IT Director. The phone system is 12 years old, the maintenance contract costs more than the system is worth, and the CFO wants a plan. Here is the exact 90-day roadmap I have used for 40+ enterprise migrations.

Days 1-15: Discovery and Business Case

Week 1: Gather Data

What to Collect	Where to Find It	Why You Need It
Current monthly telecom invoices	Finance/AP department	Calculate current cost
Number of active extensions	PBX admin portal	Size the new system
Peak concurrent calls	CDR reports or PBX dashboard	Determine bandwidth needs
Current features in use	Interview department heads	Ensure feature parity
Contract end dates	Procurement/legal	Know your exit timeline
Network topology	Network team	Plan QoS and VLAN

Week 2: Build the Business Case

The CFO needs one page:

CURRENT STATE:
  Monthly cost: £X
  Per-user cost: £Y
  Features paying extra for: [list]
  Contract ends: [date]
  Maintenance renewal: [date] at [% increase]

PROPOSED STATE:
  Monthly cost: £A (B% reduction)
  Per-user cost: £C
  Features included: everything
  Contract: month-to-month

FINANCIAL IMPACT:
  Monthly savings: £D
  Annual savings: £E
  One-time costs: £F (phones + implementation)
  Payback period: G months
  3-year net savings: £H

If the payback period is under 6 months (it usually is), the CFO will approve.

Days 15-30: Vendor Selection

The 3-Provider Trial

Get trial accounts from your top 3 providers. Run this test:

Test	Duration	What to Measure
Call quality	5 days, 20 calls/day	MOS score average
Mobile app	3 days exclusive use	Notification reliability
Support	3 calls at different times	Wait time + answer quality
Admin portal	1 hour with office manager	Task completion time
CRM integration	1 day	Auto-logging accuracy

Score each provider 1-5 per test. Winner gets the contract.

Days 30-60: Network Preparation and Configuration

Week 5-6: Network

• [ ] Run bandwidth/jitter/latency test at all sites during peak hours
• [ ] Configure QoS (DSCP EF for voice, CS3 for SIP)
• [ ] Set up voice VLAN separate from data
• [ ] Disable SIP ALG on all routers/firewalls
• [ ] Open firewall ports: 5061/TCP, 10000-20000/UDP, 3478/UDP
• [ ] Test WiFi coverage for softphone users

Week 7-8: System Configuration

• [ ] Auto-attendant: record greeting, configure menu
• [ ] Ring groups: replicate current call flow
• [ ] Call recording: enable per company policy
• [ ] CRM integration: connect and test
• [ ] Mobile apps: deploy to pilot group
• [ ] Voicemail: configure greetings and email delivery
• [ ] E911/emergency calling: register all locations

Days 60-75: Pilot

10 Users for 2 Weeks

Select 10 users from different departments. Give them the new system on temporary numbers. They use both systems for 2 weeks.

Track:

• Call quality complaints (target: 0)
• Feature gaps ("I used to be able to...")
• Training questions (document for full rollout)
• Mobile app reliability (notification success rate)

Fix every issue found during pilot before proceeding.

Days 75-90: Full Rollout

Week 11: Training

• 30-minute department sessions (not company-wide — too impersonal)
• Quick reference cards distributed
• Floor walkers scheduled for days 1-3 post-go-live

Week 12: Number Porting and Go-Live

• Submit port request (Tuesday — never Friday)
• Port completes in 5-10 business days
• Old system kept as reference for 14 days
• Decommission old system at day 14

Week 13: Stabilisation

• Daily check-in with department heads
• Review call quality analytics
• Address any remaining training gaps
• Collect employee satisfaction survey

The Success Metrics

Present these to the CFO at day 90:

Metric	Target	How to Measure
Monthly cost reduction	40-70%	Compare invoices
Call quality (MOS)	> 4.0	VoIP analytics dashboard
Employee satisfaction	> 4.0/5	Survey
Missed call rate	< 5%	VoIP analytics
Mobile app adoption	> 60%	VoIP analytics
Help desk tickets (phone-related)	< 5/week	Help desk system

DialPhone provides a dedicated migration specialist who partners with your IT team through all 90 days — from business case preparation to post-go-live stabilisation. The specialist has done this 200+ times. Your first time doing it benefits from their experience.