A dialup internet connection has very low bandwidth in the direction from PC to Internet (that is your voice data to the remote receiver). It has better bandwidth in direction Internet to PC but the problem with VoIP is that it requires good bandwidth in both directions. The symptoms are that you can hear the remote party clearly, but the remote party cannot understand you because your voice is chopped and distorted.
The solution is to use a good codec to compress and minimise the the data. The remote party will need a matching codec.
Cycom Limited uses Grandstream BudgeTone 102 IP phones (hardware phones). They are a little too quiet on ring volume and can only store one service providers settings at one time and it is difficult to dial non-numeric SIP addresses. They support G723 codec and iLBC codec which are low enough bandwidth. We overcome the phones limit of one provider by making this provider Voxalot (http://www.voxalot.com) who provide the ability to register with several other voip providers and receive DID and use dial plans to select providers for outgoing calls. We like http://www.voip.co.uk as they give a free UK geographic number.
A suitable softphone to use is provided by http://www.gizmoproject.com
Try to call us using the SIP numbers listed at http://www.cycom.co.uk/contact.html