You've defined part of your market - SOHO. Do you know which countries do want to sell in? Each country puts their own "spin" on the Certifications required before selling a product in their territory.
As background, I have been a Certifications Engineer for a large multi-national electronics company (in the U.S.) for some 15 years - mostly Product Safety, but also including EMC and Telephone Network.
There is a great benefit to be drived by having your parts selection reviewed by someone knowledgable in the product safety and EMC issues before you begin testing for the Agency Certifications. Some parts MUST have a Component Certification or else be intensively evaluated for use in your unique product. Redesign after testing frequently means the tests must be repeated and the added costs that go with them.
By the phrasing of your question, I would suggest you obtain the services of a "Compliance Consultant" to guide you through the Certification process for your first product. Some NRTL's offer this service. Check around. Non-disclosure agreements (both ways) are the norm, and expected.
For the U.S. market:
First - you will need FCC Part 15-B for radio frequency emissions. The "HO in "SOHO" forces this requirement. Unless you have the testing certification already in-house, you will need an outside testing facility. It is some 10dB more stringent than FCC Part 15-A. There is no requirement in this Standard for RF susceptibility/immunity testing.
Second - you might need what you may know as FCC Part 68 but has been reissued as ANSI/TIA 968. The second revision was recently issued. This is for products that connect directly to the public switched network network. Depending on the configuration of your products, this may be important, especially converted acoustic levels.
Third - you will need Listing for Product Safety to UL Standard 60950, 3rd Edition (a.k.a ANSI/UL 60950-2000), by a National Recognized Testing Laboratory (NRTL). The "SO" in "SOHO" forces this requirement. Underwriters Laboratories (UL) is the leader here but there are several qualified alternatives to choose from; including, but not limited to, TuV America Product Services Div., CSA International, MET Laboratories, TuV Rheinland, Intertek Testing Services, etc.
All of the NRTL's are granted their status by OSHA. Set your browser to http://www.osha.gov/dts/otpca/nrtl/index.html
for a complete list of the NRTL's. All of the NRTL's have a web presence, just search on the complete name. Most NRTL's have some limits placed on the type of Certification they can issue. Most of the NRTL's have multiple office/lab locations for customer convenience.
By the way, UL Standard 60950 is jointly published with/by CSA as CSA Standard CAN/CSA-C22.2 no. 60950-00, third Edition. This one document can be used for products destined for both markets. It is derived from IEC Standard 60950, Third Edition (1999). As such, it can give you a heads-up on what to expect when you go for the CE mark for Western Europe.
If your VoIP product includes a cable or DSL modem, there are a few more hoops to jump through.
I hope this helps.