I just brought back an iPhone from the States. Now I am looking for the best 3G plan available. My thought is basically to avoid a traditional phone plan and just use messaging and voip solely via the 3G/Internet.

My present phone is with Simyo, which is great, but their 3G tarifa plana costs 25€, which is more than I need and want to pay.

Telefonica has 10-15-25? euro plans but they require a phone contract (which I am trying to avoid). Thoughts, anyone?

First of all, note that many companies don't allow using VoIP on their 3G phone plans. I don't know if it works from a "technical" point of view but you are not supposed to use it and you cannot complain if it doesn't work.

Also all 3G phone plans have a data transmision limit. After that the speed reduces dramatically to 128 Kbps or even 64 Kbps. VoIP software such as Skype spend quite a lot of data so you reach the limit quite fast if you make a lot of phone calls with Skype.

If you think you won't spend the limit Simyo provides (5 GB), you can go to the cheapest option available, as far as I know:

Pepephone is offering 300 MB for "only" 7 euros / month. Note that unlike other companies, Pepephone won't reduce the speed after de 300 MB limit, but it will charge 3 cents / MB transmitted. The good thing about Pepephone (using the Vodafone network) is they offer 3.5G connections up to 7,5 Mbps (download speed) (I guess only available in big cities).