There are two things you might mean by "external antennas" and I will try to cover both possibilities.
The first interpretation is that you mean stub antennas that can extend to be longer. These type of antennas still exist, but mostly on CDMA phones (Sprint and Verizon). The reason they are there is because they are needed for analogue roaming on these handsets. If you read the detailed specifications on Sprint and Verizon handsets without these extend-able stub antennas you will notice they have no analogue roaming capabilities.
GSM phones have never had antennas like these as far as I know. There were GSM handsets that also had analogue roaming capabilities at one point and these had extend-able antennas.
The "internal" antennas are used now because they take less space and cost less to produce. This allows for a smaller and less expensive phone.
If you are referring to a standalone antenna that can be mounted on top of a car or in an area of good reception and then have a cable stretched to your phone then this is something that every handset can still do. If you look closely at the back of your phone you will likely notice a small rubber grommet. If you pull it out you will see the jack to plug in an external antenna. Some phone have it under the battery door, or occasionally under a sticker, but it is always there.
This jack allows for RF testing at service centers and I have used it on many handsets myself.
I hope this answers your question.