The Letter of Authorization (LOA) Process
Number porting begins with a Letter of Authorization—a legal document that authorizes the new (gaining) carrier to take ownership of your phone numbers from the existing (losing) carrier. The LOA must be signed by an authorized representative of the business that owns the numbers, and it must contain specific information that exactly matches the losing carrier’s records.
The required information typically includes the billing name and address on the account, the account number with the losing carrier, any PIN or password associated with the account, and the specific phone numbers being ported. Even small discrepancies—a suite number that doesn’t match, an abbreviation where the carrier has the full word—can cause a rejection that adds days to the timeline.
Once the gaining carrier submits the LOA to the losing carrier, a Firm Order Commitment (FOC) date is issued. This is the date and time when the numbers will officially transfer. For simple ports (single lines, residential-style service), the FOC is typically 3–5 business days out. For complex ports (multiple numbers, PRI trunks, toll-free numbers), expect 5–15 business days.
It’s critical to keep your service with the losing carrier active until the port completes. If you cancel your old service before the numbers transfer, the numbers may be released back to the carrier’s pool and become extremely difficult or impossible to recover. Maintain both services in parallel and only cancel the old account after you’ve confirmed the port is complete and calls are flowing correctly on the new platform.
Timelines and What Affects Them
Standard porting timelines are governed by FCC regulations that require carriers to process port requests within one business day for simple wireline and wireless ports. In practice, business ports are more complex and take longer. A straightforward port of a block of DIDs from one SIP provider to another might complete in 3–5 business days. Porting numbers off a PRI circuit, converting toll-free numbers, or porting between different types of carriers (wireline to wireless, or vice versa) can take 10–20 business days.
Several factors can extend these timelines. LOA rejections are the most common cause of delays. Each rejection requires correction and resubmission, and the clock restarts with each attempt. Working with your new provider to gather the exact account details from the losing carrier before submitting the LOA can prevent most rejections.
Number type affects timeline. Toll-free numbers (800, 888, 877, etc.) port through a separate system called the SOMOS registry, which has its own processes and timelines. Porting toll-free numbers concurrently with local numbers requires coordinating two separate porting workflows.
Carrier-specific quirks also play a role. Some carriers have notoriously slow porting departments, and others require additional authorization steps for large number blocks. Your gaining carrier’s porting team will know which losing carriers are likely to cause delays and can set realistic expectations based on their experience.
Typical Porting Timelines
Simple DID port: 3–5 business days. PRI number block: 7–15 days. Toll-free numbers: 5–10 days (separate SOMOS process). Cross-carrier type: 10–20 days.
Common Pitfalls and How to Avoid Them
The most frequent pitfall is inaccurate LOA information. Before starting the porting process, call your current carrier and request a Customer Service Record (CSR). This document shows exactly how your account information appears in their system. Use the CSR to fill out the LOA, matching every field character-for-character.
Another common issue is porting numbers that are part of a larger account without realizing the dependencies. If you’re porting some—but not all—numbers from a PRI circuit, the carrier may need to restructure the remaining service. This can cause unexpected disruptions to the numbers you’re not porting if it isn’t planned carefully.
Toll-free vanity numbers deserve special attention. These numbers may be routed through a Responsible Organization (RespOrg) that is different from your voice carrier. Porting a toll-free number requires transferring the RespOrg assignment, which is a separate process from porting the underlying routing. Make sure your gaining carrier can act as your RespOrg or has a partnership with one.
Don’t forget about fax numbers, elevator phone lines, alarm panel lines, and other non-voice numbers that may be on the same account. These numbers often have specific technical requirements and should be ported and tested separately to ensure they continue working correctly on the new platform.
Zero-Downtime Strategies
The goal of any porting project is zero downtime—no missed calls, no busy signals, no confused customers. Achieving this requires a combination of careful timing, parallel infrastructure, and real-time monitoring.
The most reliable strategy is to configure call forwarding on the old system before the port completes. Set your existing numbers to forward to temporary numbers on the new platform. This means calls will flow to the new system immediately, even before the port officially completes. Once the port is done and calls are arriving natively on the new platform, the forwarding becomes moot.
For organizations that can’t use call forwarding (because the old system is being decommissioned, for example), schedule the port for a low-traffic period—early morning or over a weekend. Have both systems monitored by your telecom team, and test inbound calling from outside lines every few minutes during the transition window to confirm when calls begin arriving on the new platform.
Post-port verification is essential. After the FOC time passes, make test calls to every ported number from both landlines and mobile phones. Check that calls ring to the correct extensions, that caller ID displays correctly on outbound calls, and that any auto-attendant or IVR menus work as expected. Document any issues immediately and work with your gaining carrier’s porting team to resolve them before business hours resume.
Multi-Site Coordination
Porting numbers across multiple locations adds a layer of coordination that requires project-management discipline. Each location may have numbers with a different losing carrier, different account structures, and different technical configurations. Treating the entire project as a single coordinated effort—rather than a series of independent location-level ports—dramatically reduces the risk of issues.
Start by creating a comprehensive number inventory. For each location, document every phone number, its purpose (main line, direct dial, fax, alarm, etc.), the current carrier, the account number, and any special routing. This inventory becomes your master tracking document throughout the project.
Stagger the ports rather than attempting to port all locations simultaneously. Begin with a low-risk location—perhaps a small branch office—to validate the process and work out any kinks. Use the lessons learned to refine the approach before porting higher-profile locations like headquarters or call centers.
Assign a single point of contact on both the gaining and losing carrier sides. Having consistent contacts who understand the full scope of the project prevents miscommunication and ensures that decisions made for one location are consistently applied across all locations. Hold regular status calls with all parties during the porting window to track progress, address issues in real time, and keep the project on schedule.
