If i unlock my iphone 3g can i connect it to T mobile?

Is there another step or do i just put my simcard in and it's connected

Once it's unlocked, it's available to be used on any GSM network.

You can permanently unlock your iphone without jailbreaking it here: http://gsmunlocklabs.com/unlock-iphone/

all you need is your IMEI and itunes.

No Unlocking is only way to remove the network lock in the I-phone 3G and make the i-phone 3g to accept other GSM Network sim card in it. To Unlock it specify the current network, country it's locked now? Then get the Remote Unlock service from the site http://www.unlocking4u.com/apple-iphone-3g/rs6wp9/ and Unlock it from network lock easily. Then use T-Mobile sim card in it.

Yes you can.