Cost wise solution 1 is the cheaper and more effective.
If you have full blown CCM, u generally need 2 severs at around 10k GBP a piece. This way is cheaper and more effective, tho you loose more advanced features like mobile extensions, then again in a small deployment I wouldnt worry.
Only thing, I would reccommend VoIp for a small 5 users office, cost per user works out too much, less u specifically want this setup.
Only when an office gets above 20-30 peeps do we roll inVoIP.